I would definitely contest Icies being in most peoples' '...' tier, or 'garbage' tier, or 'i forgot about them but i hear they're bad so i put them at the bottom' tier, or 'why are they in the game' tier. I mean, sure, they obviously don't have the boon of wobbling anymore, but they still have by far the most powerful options off a grab out of every character in the game. Fair being a spike for both Climbers is honestly silly. And other than the wobbling issue, they've only gotten better. Their neutral has gotten hugely better with new desyncs and the buffs to blizzard. Their already good smash attacks have gotten even better with hitbox fixes. Belay killing is so good, because it helps their MUs against some of the floaties they've historically struggled with and it's very easy to set up off a juggle and even easier to set up after a grab. Their recovery is honestly incredible (aside from synced side-b going stupidly high and Sopo side-b being not literal garbage, belay would be actually broken as a recovery move were it not for the ledge-hog glitch), and their ledge play is worlds more consistent now. Also, I think people really underestimate the improvements to Nana's AI in this game. I've been alternating between Melee and Project M Ice Climbers for the past several days now and the improvement I notice from the former to the latter is stunning. It is so much easier to keep Nana by your side in PM, and removes an inherent randomness factor that slightly held them back in Melee. They were very good in Melee, but had a couple quirks that made them 'not quite right'. This was mitigated somewhat by wobbling, but obviously it's not a perfect tradeoff, as evidenced by a significant lack of Icies placings in major tournaments when compared with the other 'Top 8'. In PM, wobbling has been removed, but with the tradeoff of having a ton of those small quirks fixed or removed along with a host of other buffs.
That said, they obviously have cons. They're an inherently polarizing character, and it takes an extremely good player not to get destroyed by proper Icies counterplay. I think the major things holding them back in PM are certain MUs that capitalize on their biggest weaknesses. The 'problem' MUs are definitely Toon Link (because he destroys them so hard and is so common) and Peach (because she destroys them even harder and is a top-level threat character despite not being quite as popular as TL). Then there are weaker MUs that have carried over from Melee like Fox, Falco, Falcon, Ganon, and Samus. These aren't unwinnable, but are noticeably rough for Icies and an additional problem because these characters are also very popular. I'd really just characterize these MUs as the Climbers' "weaker" MUs because I can't think of a better word to describe them. Then there are the less problematic MUs like Ivy and Zelda that are the same as their weaker Melee MUs in the sense that they're tricky but not unwinnable, and they have the bonus of being not nearly as common or worrisome at top-level play (at least right now).
So, how much of an impact do those cons actually have? There's one thing to be said for their weaker Melee MUs: Icies lost to the majority of the upper echelon of the roster and struggled against a few random mid-tiers in Melee, and they were still able to succeed. A few of those MUs have really only gotten better despite the removal of wobbling. The same philosophy can be applied to their weaker PM MUs. I would classify Toon Link as a pretty big problem, but a mountain that's climbable (forgive my pun, I didn't notice until I finished the sentence). Peach is kind of a huge problem, but we've seen glimmers of evidence that it's doable at a high level of play in both Melee and PM (shoutouts to Phresh, who is only on the rise against Jaden's Peach and I am certain is on his way to taking a win eventually). So they're definitely held back by their weak MUs, and the two problem MUs I just mentioned, but imo when thrown into PM they stand a better chance than, say, Melee Ganon or Doc or Luigi. Or Melee Icies, for that matter.
Make of that what you will.