UngeheuerLich
Legend
I usually think not different from you, and i guess, factotum does very fine...Wow, lots of people here approach character creation so differently than I do!
If someone asks me, "Can I make a Str/Int ranger work?" I start thinking about the issues. Okay, you give up a good ranged attack, falling back on heavy thrown weapons there. Certain dex-related feats are off the table, but that's not the end of the world. Initiative is lower, no biggie. AC and Ref will still be fine. Yep, it works - go for it!
I guess I'm not an optimizer. Heck, my favorite character is my bard, Factotum, who tried to be good at everything. Every feat is a multiclass feat. His stat array is all 13s, with a 14 in Charisma (post-racial 16, since he's a human). He is not a wrecking ball in combat, but he gets by just fine. And he's a blast to play. All of the other LFR players at my store know Factotum and look forward to being at a table with him, rather than dreading the fact that he might not be as razor-sharp in combat. He gets the job done, and he's fun.
So, to the OP: Yes, your Str/Int genasi two-weapon melee ranger can work just fine, and he sounds like a character with lots of cool possibilities. I say go for it!
but AC 15 is terribly low for a frontliner, whose saving grace is only his extraordinary attack bonus...
You don´t even get a damage boost, and your extra damage only triggers once per turn (assuming twin strike)
So, while I would not mind playing with this ranger, I would still worry about him, as I assume, his most prominent status is dying, as he will be the most fragile and most threatening combatant on the field.
Low constitution means no hope for improved AC late on, and no stat points to spare to increase wisdom...
So if he asks for an advice, I give it...
And going 18Str, high int and a bit constitution will serve him better, as his character will be highly damaging, tough as nails and extraordinary because of his high int and probable multiclass options/good skills...