Right, but you're looking solely at weight class. There's more to survivability (and, thus, 'glass'-iness) in Smash than weight class.
Think of recovery like health recovery moves in an rpg. You get knocked off-stage, but you can recover back onto the on-stage fight by getting back to the stage. Having a good recovery is a way of extending your stock, whilst having a crappy recovery means you have poor/no means of extending or preserving your stock when knocked offstage.
This is similar to restoring some HP in LoL or an rpg - you extend your survivability just a bit to try and stay in the fight. Some characters in rpgs are easily killed, but they can utilize healing magic to actually have decently high 'survivability'. This prevents them from being a glass cannon, meanwhile the flimsy fire mage that has 0 armor and 0 healing and mediocre mobility is most definitely a true glass cannon.
Meanwhile some characters have a poor recovery but high weight - this is simply survivability balanced differently within the character. Bowser's ability to be easily taken advantage of makes him, in many matchups, more of a 'glass cannon with low actual survivability' than sheik. Smash is weird in this way.