Thanks for all the advice so far. A few things:
1) I examined my motives after I wrote that first post. While I don't think I was consciously jealous, it did occur to me that when I initially joined this group, I wanted to make a swordmage. When I was informed that the group already had a dragonborn swordmage (and another defender on top o that), I thought, "Well, dang, guess I'll make something else."
I'm not into the whole Freudian thing, but I guess it's possible I was subconsciouly over-critical of the swordmage because I wanted to play one myself. I'll err on the side of caution and keep my criticisms to myself, for the time being.
2) The group is running through published modules, like Keep on the Shadowfell, and all that. These are pretty widely known for being a hack-and-slash fest with minimal opportunity for non-combat-oriented RP, so I have to say I don't think it's unreasonable to expect every character to pull their weight. In any other game, though, I'd agree that a +3 to Diplomacy could be more useful than a +1 to hit. But in this game, I honestly thought we had more trouble clearing out kobolds than we should have.
3) I would be... surprised if this guy went with low Int for 'roleplay reasons'. He didn't seem to roleplay much at all, mostly keeping silent unless it was his turn in the iniative order. On his turn, he basically just said, "I use <power> on <target>." He really seemed to be somebody new to 4e, and possibly new to D&D in general. In the first fight, the DM had to explain to him how to add up all his bonuses to make an attack, for instance. A lot of the group seems to be newer players.
4) It is true that there's different ways to building a character. I later discovered that he was using a greatsword, bringing his Warding bonus down to +1... not something I would personally do, but then again, I'm sure there are greatweapon-using swordmages out there. As to his internal logic to creating this character (I deduced that he has an 18 Str, 16 Con, and 14 Int), I think outsider has a pretty good theory:
Here's my guess why he has low int: He's playing an assault swordmage, and didn't notice the Intelligent Blademaster feat, thus he improved his str instead. It's also possible that he thought it was a waste of a feat.
That's a good point, and it's a mistake I very nearly made with my first swordmage, who was also assault. This guy is, in fact, an assault swordmage. So, that may be it.
Anyway, in the end, I realized that this was only one session. And even though he missed a lot, he did contribute to the group (mostly by having a big ol' bag of hitpoints and healing surges, and by getting some lucky rolls with Flame Cyclone and cutting a swath). If he asks for advice, I'll be more than happy to give it. Otherwise, I'll give it a few more sessions, and then maybe (possibly) email the DM.