I do actually quite the opposite.
True is that I relied on pistols and sniper rifles for most part of the first playthrough.
But later on I started finding amazing SMG (that I felt that rendered pistols useless) and, as enemies kept getting tougher, sniper rifles didn't seem to be as useful as before, so went with shotguns instead.
What I have usually equipped is a SMG (up in the d-pad), shotgun (left), sniper (or some other SMG with different elemental damage, down), and rocket launcher (right, and that I use mostly to get out of extreme fight for your life situations).
That's interesting because I've definitely found the opposite to be true. Since there's basically no such thing as an SMG that does higher per-shot damage than a pistol, I find that it takes more
time to kill with an SMG than with a good pistol. And increased time to dispatch an enemy increases your own risk and of course drains ammo quickly.
To that end, I've found pistols and sniper rifles to always be the easy solution. So long as you can aim, can keep some distance between you and the target, and know where the critical hit points are (arm joints and red dots on loaders, heads/tails/eyes on humans/animals), they both wreck *everything* faster and more accurately. Siren's skill made that insanely easy, but it's about the same for everyone. The only time I ever feel like I need to have a shotty is if I'm fighting threshers. SMGs and AR's...I break out purely for a different experience, if I want to save SR/Pistol ammo, or if I need all the ammo available to me to kill a boss.
Think I have some pretty good AR's and SMGs...but I find it takes 10-20 rounds of SMG/AR ammo to equal the damage of 1 equivalently leveled, high-quality pistol. And a SR with crit...fuggadabouit.
just my experience, with my second character almost to 50 and one of just about every legendary in the game found.