I think your comment about the weapons and your comments about ammo are at odds. The very reason to not pick the latest-greatest sniper rifle is that it only has 12 shots. The starter assault rifle also offers much more ammo than the five-round-burst model.
The only sniper rifle that has more than 12 shot capacity does 1/4 the damage per shot... and conveniently holds 48 rounds. The rapid-fire versus single-shot is the argument there.
And I can't comment on assault rifles, the only time I used one was on my Normal playthrough, where ammo is NEVER a problem.
The intention behind the ammo is that since the heat sinks are usable by all weapons, the player is supposed swap back and forth between weapons frequently to avoid getting low on one.
The game is generous with ammo *between* fights. It is very lacking in ammo DURING fights. On Insanity, it takes 1.5 clips with the fully-upgraded pistol to drop the Armor of *one* husk. Keep in mind that they typically spawn in waves of 3 to 5. One particular fight (at the end of the IFF mission) has you killing 20-30 husks and abominations per 'round', THEN hammering at the core. To be fair, after each round of this, some ammo clips respawn... usually four or five.
I have literally emptied every single gun I carried in fights before. Thankfully, I could still fall back on Adept-powers. And your teammates, of course, never run out of ammo.
The final battle took all of my submachine gun ammo (725 rounds), all of my pistol ammo (24 rounds), all of my sniper rifle ammo (48 rounds), and *FOUR* shots from the Cain. (A certain enemy drops heavy weapon ammo when killed, trying to avoid spoilers here.) And all of my guns ran dry multiple times, as there is ammo you can collect from fallen enemies during that fight.
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I think the biggest problem in ammo discussions is difficulty setting. On Normal mode, as a soldier, I cruised through every fight I entered with plenty of spare clips and OCCASIONALLY switched to an assault rifle when I would have preferred a sniper or machine gun.
On Insanity, I was constantly out of ammunition for all of my guns -- and I'm a pretty practiced FPS player. Not every shot is a weak-point shot, obviously, but I rarely wasted shots on bulkheads.

I think there's a lot of room between "you have unlimited ammo" and "you get two clips". ME2, especially Hardcore and above, really felt like I had no ammunition, regardless of weaponry. YMMV, obviously.