Placement games in general are pointless. I've seen people go 1-9 in placements and get placed in gold. On the other side of the spectrum I've seen people go 8-2 in placements and get placed in bronze. Point being, you are already placed within one or two tiers within a ranking before you even start your placements. So it absolutely is a waste of time. It's to create an illusion that you have some say in where you get placed. When truly those 10 games mean literally nothing.
If someone's mmr was around silver 3. if they went 8-2 they might get placed silver 2 or 1. If they go 2-8 they might get placed silver 4 or silver 5... big fucking whoop. It's a broken system, especially since most people have to go through a bit of a learning curve before they start figuring the game out. I literally make alt accounts often on games like these because first account I'm learning game so my mmr is lower, second account I always place higher and save myself the pain and struggle of trying to climb out of hell. It would be nice if we didn't have to exploit a broken system.
edit: I realize i committed one of my pet peeves here, stated a problem without even attempting a solution. Soooo. How about just making everyone start in bronze 5 and climb up. Cuz lets be honest here. I'm not the only one who does some off the wall stuff in normals... AP varus, AD lulu, Vayne top, etc. stuff I wouldn't do in ranked. That should have no effect on my mmr whatsoever. I think normals is the place you should be able to do stuff like that without fear of tanking your mmr. But as it stands, you almost have to take normals as serious as you do ranked, which doesn't help the already toxic as is environment that mobas can create.