I would say, Ganondorf is probably the worst example of a boss-to-playable transition in the series, and one of the poorest representations of a character in Smash. Nobody is happy with his depiction because he's Captain Falcon wearing Ganondorf's character model.
Would you be happy if Ridley received that sort of treatment? I don't think I would be, but more to the point I suspect Sakurai might not be either. As the main series villain of Nintendo's third largest franchise, Ganondorf is very much obligatory and therefore can get away with such a shoddy portrayal. It's Ganondorf, he's gotta be there, accurate or not. Ridley is very important to Metroid but Metroid is less important overall, so including a villain is less of a priority (not to say it isn't a priority at all, but it is less so than Zelda).
Some people support Ridley so strongly that ultimately they don't really care how he ends up, which is fine, but I don't believe Sakurai is one of those people. Ridley's appearance in Brawl is probably a good way to gauge how Sakurai thinks Ridley should be portrayed. Whether you agree with him or not, it would be very difficult to accurately recreate that incarnation of Ridley as a playable fighter.
I see this idea that Sakurai is 'teasing playable Ridley' a lot, and people questioning why he wouldn't just show him as a boss straight away compared to other deconfirmations, but... are you sure he isn't just trying to, you know, let you down gently? Showing Ridley right away as a boss would hurt and Sakurai probably knows that. Maybe after the direct he was expecting people to go 'well, I guess he's not playable' and start winding down the expectations. It really might not intended as teasing at all.