Smash at a competitive level? The game hasn't even been out for 2 weeks. There isn't even a tier list at the moment. It's guessing. Calm down.
who needs a tier list? is a tier list going to tell you who you are good at playing and who you need to practice with, and who you just don't like playing? probably not, and with the updates constantly coming out as the game is updated and new content is added, the meta with inevitably change faster then a tier list could keep track of. get over the idea of tier lists and just focus on playing the characters you have fun with, who do things that enjoy and like to practice doing, that's how you learn to play them better, and how you stop making complete dumbass coments like you made earlier. no offense, but if you don't think he's good, then play someone else. That, or practice with him until you can use him well. there's no use in complaining that he's bad, either practice or play what you think is a "good" character.
a bunch of inacurate information in bulleted list form.
right then:
1. he's not a camp character. his canon is more for punish and offstage harassment of characters with horizontal recovery.
2. the reason moves are safe on his shield is because he's got low traction like Luigi. nowhere near as low, mind, but still lower then others. and if you're only using his grabs out of shield and not mixing things up to get grabs, then you're using the grab wrong. He actually has some decent range on his grab, and if you're not just shielding a hit and hoping to counter-grab, then you'll learn real fast how annoying it is to deal with a bowser jr. that can dodge behind your slow-ass falcon punch and grab you, or punish a short dash attack with a grab.
3. try short/full-hopping a mechakoopa and either picking it up, or running after it. down-b into side-b is an approach. if they dodge the koopa, you hit with the cart, if they jump, you jump into aerial. they shield, you jump short and either go into aerials and back off and try something else. he's got plenty of approach options, you just need to be ready to use them.
As for spacing, again, Mechakoopa and canon. both are great for creating space and zoning. learn to drop a mech now and then and you'll be fine.
4. he's got a good enough recovery to loop the underside of a stage. I honestly don't know who you're playing, but it doesn't sound like bowser jr. you get knocked away, double jump, pop out the cart, hop out of it into your up-b. you can recover low and safe like that. And as long as you know when to preemptively jump from your cart, you won't be killed while recovering. not easily at least.
5. the smashes being DI'd out of only really works with the disjointed hit-box on his forward smash, and only if they're already really, really close to you to begin with. if they're that close, up-smash. as for kill power, all his aerials, save Dair and a sour Nair can kill easy. I've killed around 100% or so with a well places Bair, even lower with a sour Fair when edge guarding. his side smash can kill below 100%, and his up-smash, I believe tends to kill anything at or above 130 at the point of the final hit. that's not too bad. oh, and let's not forget the down smash. if you can land it properly(read predict a roll), then you can launch your opponent very, VERY far. you mention the down-smashes hit-box? yes, the hit-box is low and digs into the ground, but again, it's his down-smash. It's their to punish ledge hogging and rolls. it's got a lot of launch power in it, as long as your target is below you or standing on the ground.