Lol, Asta is among the easiest matchups for yoshi, you guys have no idea what you're talking about. and advice like punish FC 3K with low grab shows just that.
zombie: use stances on wake ups not out in the open. 4A+B, 214A are even stronger against Astaroth than other characters. 66B is a good long range safe TC and FC 3K stops asta from moving around, forcing him to crouch (shuts down all his options) or trying to keep you away which is not hard to deal with if you anticipate). Thus asta will be under constant pressure. Its pretty easy to force your mixups on him. Thanks to iMCF Asta cant even counteratack after blocking your moves. You can just pwn him spamming this. (3A_B+G is crap, both slow and breakable, even if Asta connect this you can still guess right, and if he wiffs it, its big damage) Also Yoshi wake up game is far superior to Asta's. Well. thats not that a bad matchup, but definitely favorable for yoshi. Especially if asta spams variety of throws as suggested above. lol.
jargen: I didnt get what kind of moves you have problems with, but mitsu might be a bit intimidating due to his 1A that asta cant punish. To me this matchup appears relatively equal, maybe with a slight advantage to mitsurugi. If you can name exactly the moves or strategy that gives you trouble i'll help out. Same goes for raph, whats a thrust combo? (4B~prep?)