What on earth is going on with match making?

I've played League casually (ARAM, bots, rotating game modes etc.) for a while but just recently starting getting into pvp, hoping to improve. I've been playing normals and I have to say...it's bonkers. Since just last night I've had 4 matches where it's been all bronze (and maybe one gold or silver) vs. golds and at least 1 plat. Most recent match, 5 bronze vs. a 3 man premade (top, jg, and AD). Jg was platinum, their AD was gold. And. It. Keeps. Happening.

These games were over before the five minute mark. Over a dozen or so matches, only 2 haven't been complete curb stomps. It's bronze, they're just normals, who cares? I'm new, I suck. I expected as much. I don't care about losses. I care because it's not fun to lose (or win) this way.

Is this just to be expected? What's the typical rank/premade distribution for your games? Is disparity this common in ranked too? I'm new to pvp so my sample size is small but so far the match quality has been absolutely horrendous.