I don't think it is AS bad, but if the logic for Dreamland is "its just too huge", then how is it fair to cut down on that without cutting out the other extremes?
The following is about YS vs WL, not about including both in a stagelist.
The extremes are different though, like you said you don't think it is AS bad.
Dreamland is much more of an outlier than any other discussed stage.
YS is
barely different than WL. Almost identical ceiling, YS has a
slightly smaller base width, YS has
slightly larger horizontal BZ.
But there's one where YS loses hard, and that's actually the least talked about stage attribute: the bottom blast zone. YS is really really shallow and IIRC it makes sweetspotting certain recoveries near-impossible or actually impossible (GW and Sonic come to mind, and CPU Fox will die when he tries to sweetspot from below ledge so...)
For the purposes of attribute sizes, I'm saying they're negligibly different except WL has a
much preferable bottom BZ.
Then there's "space" where I really don't see that much of an issue. They serve the same purpose for most matchups in this regard, I don't find WL cramped compared to YS either.
Triplat. It's not a deal breaker but it's just another factor. Why add in another triplat when WL offers a unique layout?
Sloped ledges. As a Wolf main they're fun as hell but they make some edgeguarding tools wonky and make wavedashing (especially to ledge) wonky too. That's a lose for YS.
And finally, Randall. I think of him as "pseudo-random" because while he is on a timer, A) almost no one memorizes it and B) it's up to the flow of the match whether you or your opponent will be offstage in a situation where he'll interfere.
And of course how he messes up tethers.
So like, individually, the problems of YS are quite small. This sounds hypocritical because I've argued against small discrepancies for Bowser's Castle in favour, but here's the difference: we have a 100% viable, near-identical stage that serves exactly the same purpose and is classified in all categories the same, in WL. We don't have that for BC which is why in the past I've responded to the discrepancies of the stage (emblem, chains, fire, platform height).
Bottom line is, YS has a few little things that add together and make any sane person wonder why WL has been replaced.
The only reason WL could be outed by YS would be if it still had the minigames.