If a character has super bad mobility, no amount of frame data can change the fact this character's DA is held back, SHFF game is held back, zone breaking ability is held back.
Unless the character has super long range, absurd projectile, and crazy rewards. I mean, the description sounds a lot like Luigi, except his ground speed is below average rather than 'super bad' but his moves not coming out that fast. He has bad approach game and shields a lot. But I can tell you this after maining the character for a year, rewards can be crazy, but mobility will always be an issue.
Bad ground mobility means you can't chase people at all. Dash attack and dash grab are held back due to how slow they are. You can't get into your juggling position comfortably and tend to struggle against projectiles due to the time it takes to just reach people on the other side. Your punish game will also be hindered.
Bad aerial mobility means you're a juggling pin. Doesn't help since the character is implied to 'have low end lag (But NOT landing lag)', you can't just falling aerial something. You can't extend combos and SHFF game will be suffering, even with the best set of aerials. You will also have a bad time offstage, not being able to move much. And every time you are jumping to the air, you can't chase airdodging people easily.
I mean, we all know what pre-patch Luigi is. Bad mobility but crazy rewards. He lose too hard to Sheik and Rosalina to be solo-viable even when he kills them at 90% simply because he can't catch people (Sheik) or get through camping and projectiles (Rosa, Mega, Pac, you name them). Considering Smash 4 is a reign where mobility rules, I don't think this particular character will do good. All people need to do is just to shove disjointed stuffs and run away to camp to beat this character, because they have no reason to approach and stay in his face. Sheik and Rosa will pretty much ROTFL this character.