The "sun" inside Baam seems to swallow everything he absorbs, so it seems likely that is the reason for his copy ability. And if it is as theorized "the outside god" then he wouldn't have his copy ability.
His immunity to spells and straight up destruction of them is likely due to the spell that was used to bring him back to life/seal the god inside him. So he wouldn't have that.
He would be restricted to a limited amount of shinsoo because he's bound by contracts like everyone else. (Of course he could still be making shinsoo contracts, but I highly doubt it.)
His physical strength should be the same, so lacking compared to other DD. But he could still make up for it with reinforcement and to a lesser extent, training.
GoG wouldn't have trained him, so no 2nd lvl reinforcement. (As a regular.)
Jinsung wouldn't have trained him, so no flare wave. Unless V invented it / could use it.
Assuming V and Arlene aren't trash parents like the rest of the FHs seem to be. He may have been taught spells and Tension.
Evankhell wouldn't train him, so his orb wouldn't be huge. (While a regular.)
Baam WAS born in the tower, he just left it (maybe) and came back. So his talent should be the same, but his potential/limits would be considerably lower.
As a regular I expect he'd still be capable of making top 10 in E, D, C and B, unsure of A.
As a ranker he would be one of the oldest DD in the tower, assuming he survived to the present day, I expect he would be top 100. Probably a floor owner.
I can't remember if Baam's loop is only possible because he's a irregular or because of his shinsoo blessing. If it's the latter he could be a tower born actually capable of fighting the FH's. If not I expect he'd be above Kallavan below Adori.