66A is pretty bad. Punishable, high, deceptively short range, and worst of all, zero okizemi after it hits. He has no way of discouraging back techs after 66A hits (not even 4B+K works because 66A's recovery is too long), and back teching after 66A puts you right at a range where he can't really do anything except maybe back off and fire a bubble or two--he's not at enough advantage after 66A knockdown to work a run up or QI mixup. His AA has average reach and 623B's risk/reward is in the opponent's favor. Also, his frames do matter with 623B as the TC is too slow to go under fast highs (like Leixia's AA); at anything worse than +1, 623B loses to Leixia's AA. It's also JGable/steppable on reaction for a 44(A) punish.
623A is unfortunately no longer 623 in SCV. It's now 33A, which means it's a hell of a lot slower from neutral. It functions more like Nightmare's 33B than an actual stepkiller; if the opponent whiffs something while you're 8wayrunning, 33ABK is what you nail them with.
The 2nd hit of QI A+BB can be stepped and punished with 663BB or even 662kAAK if you're close enough. If he just does one bubble and you block it he's at -38 so run up and do whatever you want. The startup for the evasive frames is somewhat slow so QI can't be used to evade many of Leixia's frame traps.
Algol's backdash was the best in IV. In V, it was nerfed considerably and is actually pretty damn bad--one of the worst, unfortunately. Off the top of my head, the only 44B force block I can think of is QI B → 44B, which requires giving up guaranteed damage with 3B BE. Unless he GIs something when you have no meter for re-GI (not very likely considering the disparity in meter gain between the two characters), if you get hit with 44B it's because you fucked up severely.
Am I saying Leixia rapes Algol? Of course not, I'd probably get lynched if I said Leixia has any matchups better than 3:7 here in the Leixia SA. But this matchup can really go either way.