You want to know how bad the soulborn is? A non-meldshaper, using only feats (Shape Soulmeld, Open X Chakra) get binds before the Soulborn does. Which means that a character without a single meldshaping level can bind, say, the Fearsome Mask before the Soulborn itself can.

I'm sure there's some good houserules you can use to get them up to par... but just a small Smite fix isn't going to cut it. Off the top of my head, I'd say that you should keep the Smite fix and shift their entire meld/bind table down, oh, three levels or so. If you insist on keeping them at the paltry number of melds and binds (which isn't entirely impossible to keep useful if you give them really nice Smite bonuses and similar boons), at least give them their smaller doses at a level that would still be useful. Keep their meldshaping more akin to a bard's spellcasting than to a paladin's.