I have personally played enough times vs Kabal and Jaime and I don't find this matchup to be incredibly good for Yoshi. I wouldn't call it a wreck as I believe Yoshi is only > over Samus and not >>. Yoshi has issues comboing Samus. Spamming b -airs doesn't work as Samus has enough range with her b-air to counter this. I also find d-air reads difficult to get out of as Yoshi as Yoshi just doesn't seem have a good get-up function to get away from reads (why I dislike the Ness matchup personally). Samus's n-air also seems quite useful in this matchup.
I've played it with JaimeHR and Kabal too. Kabal is pretty easy to beat in this match-up. I had a harder time with JaimeHR but that's more of him being a better player.
I think it's >, not >> too. Wreck was probably an exaggeration (I did throw in the "relatively" though), but I still think it's Yoshi's best match-up.
Issues comboing? Samus is like one of the easiest characters to nair chain, and dash attacks are a useful tool too. Maybe Samus doesn't get as combo'd as hard as some of the heavyweights, but it's not a disadvantage when you consider Samus's awful combo game lol. Most characters have issues comboing Samus; in fact, Yoshi is probably one of the better characters at comboing her.
You shouldn't be trying to outrange Samus's bair (although you could use neutral B if you really wanted to). Wait it out slightly outside its range, and attack right after it ends with a dash attack/djc bair.
Parrying can help get out of techchasing situations/pressure situations. Speaking of which, Samus is the easiest character to parry in the game, and has a very hard time against it. I heard you don't even parry, so that may be why you don't find the match-up as easy as I do.
Samus's nair? Wat
I agree with Luigi being pretty advantageous for Yoshi too, probably Yoshi's best match-up after Samus.
I reckon Yoshi has the advantage on Samus, but probably not his best match up.
And I agree on Ness-Samus being even too.
I don't agree with Ness having an advantage on Yoshi..especially not on Dream Land. If you avoid DJCing into Ness' uptilts you should be fine.
What do you think his best match-up is (inb4link)?
Well, I said slight advantage. Most of this is based off both my Samus and Yoshi going pretty even with Peek (on Dreamland btw), and my Yoshi is definitely better. I've also beaten Sheer with Ness, which shouldn't really happen. I did think it was even for a very long time, and I could still see that, so I'm not too adamant on Ness having a slight advantage. I also have more experimenting to do with some stuff.