Well they gotta come up with the moveset, weapon, story, design, etc for a new character. A lot of that is largely done for any returning character.
I dont know, i havent personally liked a lot of the new characters introduced in this series. It seems as if identifying what might be wrong with an existing character and making changes is far more possible and easy to do than designing a likable, new character completely from scratch.
Indeed, beyond that, there is the fact that they already have an established narrative and if there is anything that defines the apparent design priorities for SCVI to date, its the nostalgia factor. Everybody included in the roster so far is a SE-SCIII character, and every plot device is something culled from the the span of time covered from roughly the tail end of Soul Edge through the early/middle of SCII, with some characters (Talim, and probably with Amy and Cassie when they drop) even as late as the beginning of SCIII. There's also two new characters who play a central role int he story, and that's perfectly par for the course in SC: one or two of the new characters are always among the headliners for that title; in SCIII all plot lines revolve around Zasalamel and to a lesser extent Tira, in SCIV it's Algol, and in SCV its Patroklos and Pyrrha. But aside from those two and the guests, it's proper a proper nostalgia fest. It doesn't surprise me in the least that we have six forecast characters in the code, whose names all roughly align to the remaining six characters from the narrative arc stretching through the first half of the franchise history.
Now some of us may wish for different characters first, and fair enough--I get that impulse; I never mained anybody in those characters and don't expect I will enjoy playing many of them very frequently. But you know what I will enjoy? Playing against them. And I'll buy them for the rare event of wanting to play them, the less rare event of having friends over I know will want to play them, for characters creations to share online for whom they are the most ideal fit, moveset wise, and for a half dozen other reasons. People forget there are lots of reasons a given player will buy a character that they may never main and who they would never pick in a "pick your one favorite" poll, not the least of which is that same nostalgia factor. From a purely self-serving perspective, I suppose I'd choose to have Hilde or Viola or Natsu back before a couple of those classic six characters, but I have to say there's a certain kind of logic and stylistic appeal to them filling out the legacy cast first for this game, and that certainly fits with every design cue the devs have given about this game to date.
Besides which, there's another pragmatic piece to this. In order to believe those names are not who they seem to be, we have to believe Namco is actively trolling it's consumers for shits and giggles by throwing in these clearly misleading code names...I mean, what could they possibly stand to gain by doing so that would compensate for sowing so much ill will among their most loyal and engaged customers. We're talking about a sophisticated company with a carefully calculated marketing strategy, not some rinky-dink indy operation playing pranks on their patreon funders. Ever notice what Okubo is always saying whenever people ask him to spill the beans on confirming the upcoming season one DLC characters (even though we know who they are, and he knows that we know) or to give a hint as the to the release timetable? "Oh, I don't think my marketing colleagues would like that very much." We're talking about a Forbes 2000 company here--in Japan no less. You best believe that shit is real. If you walked into a meeting saying:
"I'd like to massively disappoint tens of thousands of our consumers by teasing a few of our classic characters for Soulcalibur VI's upcoming content, but as a bait and switch for other characters--you know, for lawls! So anyone hoping to play them again will be disappointed, and rather than creating hype, we'll create a massive amount of bad will right when we're gearing up to promote that same DLC. Game fans are a famously easy going and forgiving group of consumers though--I'm sure they'll see the humour of it!"
...well you might as well pack your desk ahead of time, because you'll probably be escorted out of the building after being given your pink slip, said escort being so that you don't accidentally f#$@ something up on your way out of the building.
Anyway, echoing your comments and those of
@TresDias, I don't have to love playing a given style or the character design itself to see it having a meaningful place in overall gameplay tapestry of the series. A character could by fortieth place pick for a main and I'd still be happy to see it back in the fold. Beyond that, if the game doesn't gel together, no amount of clever characters will save you from the complaints. In every respect this makes classic characters simply easier as known commodities--not only does it involve the lessened costs and development time that you note above--everything also fits together just a small bit easier, from gameplay balancing to fleshing out the single player content. The design priorities for this game is such that PS wants to somewhat re-invent the wheel...but they also want that wheel to look super familiar to you.
And like you two say, one doesn't have to like every design. I think I've liked five of the last sixteen main roster characters released since SCII. But even the ones I didn't care for initially I've gotten used to and miss when they are absent. I mean, for crying out loud, we've had a goth chick who fights with a hoola hoop for four games running now, and we just accepted that shit like it was perfectly normal. And you know what, ridiculous as she is, I'd miss Tira if she were gone, because I've gotten used to that unique dance between her and my mains. Same story for the Classic Six, except except I've been missing most of them for a game longer since they all got the boot from SCV (SCIV for Li Long). If I play Rock twenty times in the next five years, it will still be more than worth my contributions to the DLC coffers to have him back in the mix. Same for Setsuka, and Hwang, Li long, Yun-seong, and Lizardman.
I also understand that if I want to keep the gravy train flowing and give a remote, remote chance of there being a third season pass, I need to not allow myself to get too picky and entitled about the choices of season two. The devs will choose who they are going to choose and if I'm not happy with their choices, I'd only shoot myself in the foot if I get so self-involved and judgmental of their choices that I don't buy it, thereby very slightly reducing the chances that my favourites would come in a third season. Maybe some people would say that makes me a non-discerning consumer, but I don't think so--I just want the biggest Soulcalibur game possible, including the biggest possible roster. Two months ago, I was thinking there was only an 80% chance of a second season, and now I know there's almost certainly going to be one. I also thought it was going to be four characters for sure--now I know it's six. Whoever they release I'm going to buy, and on all three platforms. Then I'll probably buy some as gifts for friends. I doubt everybody's going to splurge like that, but for me, I more than get my value considering how much I am going to play this game. In any event, whatever the motivation, I suspect there are plenty of people who will buy any legacy character in a heartbeat, whomever it is.