Are placements based on more than win/loss?

So I've been getting into my placements and I've heard a lot of different things like people winning all 10 games and not getting the rank they were or some people getting dropped a whole tier just because they lost 2 games in their promos. Another thing I heard is that you can't earn a higher status than your last placement, but that can't be true because "imqatpie" is Challenger 1 right now unless he literally went from like Challenger 5 or Master to Challenger 1 in a couple days...

I was wondering if placements are based a lot more than just a win or loss. If not they should be. My last game I lost simply because our team comp. didn't have wave clear. We were owning in team fights and even aced the team multiple times, but I was playing Tahm support and the rest of the team were basically single target champions that couldn't wave clear at all so we just lost to enemy split pushing. That's how I feel a lot about this game though. You can do really good in game and not feed, but so much of it comes down to team comp and if you get afk or troll on your team.

So do you think placements are based more on personal status in-game rather than winning or losing the actual placements? I mean did everything perfect as my role in that game and even had over double the assists than the enemy support. I also was keeping map awareness with wards while the enemy support didn't even buy sightstone, but there's only so much you can do as Tahm support. If the rest of your team can't push waves worth shit you're pretty screwed. Literally by 30 mins we only had like 1 enemy tower down and we had like 20+ kills over the enemy, that's how bad our wave clear was.