They end up looking boring then. They all have barriers/shields to stop bullets anyway - that's what really offers protection. A bullet fired from any gun in the MEU will tear through any material, including armour - it really doesn't offer that much protection. If your shields go down and you're not in cover you're pretty much dead no matter what you're wearing.
Read up codex on Armor/Equipment. The armor itself won't protect you for long, true. But even a brief protection is better than none.
One of the most important additions to combat hardsuits is medi-gel application to the wound, done by a suit's VI. Outfits of Jack, Samara, Thane, Zaeed won't be able to apply it to exposed areas. Jack arguably gets the worst of it.
Regarding boring look, do you really need to see someone's as and/or ****** in combat for the game not to be boring?
I like the design of most ME2 outfits but I think that they would be suited to off-duty rather than combat sequences. And armor can preserve character's uniqueness. Look at Miranda's outfit from Alternate Appearance pack, Ashley's combat armor in ME3.