Yeah, he's bad but not the worst. His recent buffs in 4.0.0 have helped him out a bit. Fixing the jank with his downair after being hit, his recovery is faster and has a bit more distance to it, dash attack got even BETTER when it was already insanely good at it's job at killing unsuspecting opponents and his upair got more consistent with the sweet spot and even better knockback to boot.
He's still a solid threat but he will never have the jank or high tier attacks like the swordies. Still, he is a spacing demon. His tail attacks reach far, hit for decent damage and can combo/combo start. Back air is deadly as is Up-Smash (Which also got buffed). Command grab for mix ups (Also buffed) and great edge prediction coverage with F-Smash (Still stupidly strong) and the buffed Up-Smash.
His projectile isn't super great though has its uses. It forces favorable positioning when opponent is off stage, can poke enough off stage that most characters die if they get hit by even one fireball, can shield pressure (If they block they have to parry the last one otherwise you can rush in for a grab) from moderate distances, and so on. He can't go ham like Pika or swordies or even Palu (With constant back air pressure due to her ridiculous invulnerability on the shield). Yet he can keep up pressure just by being a personal space invader and threatening KO's at pretty silly percents.
Personally his size isn't the factor of WHY he's lower tier. It's part of it but not the major factors. It comes from linear recovery (So predictability) and ease of edge guarding him and general collapse under heavy pressure placed on himself. He has a few 'get off me' options but not enough and they become predictable. So....the key word is predictability when it comes to Ridley. He can fall apart if your opponent gets too much momentum, yet he dominates if momentum remains on his side.
I feel he's just 'fine'. I don't think he needs to get too much 'better'. He feels fun to play as he is now and I, personally, dislike playing characters considered 'too good' as it often feels demoralizing when people tout any wins I get were due to the character, not my own skill. If Ridley got the top tier treatment, I'd feel less prone to playing him which would suck. He's fun to play with enough going for him that keep him a modest threat but not unfun to play against.
If anything though he can only get better from here. Patches so far have given him more and more, unlike K.Rool who just gets pooped on every patch XD