I can truly say that the Royal mega ships (at least Oasis and Quantum class, I haven't done Icon yet) don't feel crowded because they're laid out very well and Royal does an excellent job managing guest flow so you really never feel like everyone is in one spot at the same time. NCL Breakaway is smaller and actually felt worse due to some weird layout decisions; tbh people who think the Wish is badly laid out need to go on that one and they'll really see a badly laid out ship lol.
My issue with Royal is more so the nickel and diming feel, the post-covid cutbacks in MDR in particular basically force you into specialty dining unless you want to eat at the Windjammer the whole cruise and then you have to look at specialty dining packages. Drink packages are absurd. My sister has high C&A status with them so some of that I get to mitigate but on the whole, while I very much enjoy their product (I think they're the only other line that begins to approach Disney in terms of entertainment quality, specifically) and would continue to sail with them in the future I generally like Disney better. Virgin is next on my list to try after the Destiny.
I'm with you though tbh the only ships I would avoid altogether are older ones as the newer ones tend to have more amenities and things to do but even then, I would never say never. Sometimes you just want to get on a boat and if the price is right I would. (Except Carnival. That is one line I avoid altogether just because I am not at all a fan of their overall product.)