You're speaking without experience, surely. I've been playing it for years and many master-strength players prefer 3. d4. In naive hands, 3.d4 leads to pitfalls for white but in the hands of a strong positional player, black's forces can be cut in two after the ...e5 sequence. I don't play it and really, how many games have you played with it against decent opposition?
Three games (as Black), all starting from the move order 1.e4 c5 2.d4 cxd4 3.Nf3 a6. No problems at all.
3.c3 and 3.c4 are better choices. I would prefer the latter, especially if white likes to meet the Kan with 5.c4. Under the O'Kelly move order, white can achieve the same positions cutting down some of the good white options (since d4-d4 can be played at the most appropriate time).
Try d4, if you're a good, positional player. c3 and c4 are similar. g3 is superior to them both because in that line .... a6 is genuinely wasted as black normally plays Rb8 anyway. But d4 is the strongest move. However, nobody bothers to really analyse and study it. They assume the stuff about e5 being equal is correct, but it isn't.
In that case, you do not know the openings you are playing: 3.d4 is surely enough a rather straightforward equality for Black