That’s what already happens. At the start of new season you have to do placements again. Rank reset.
If you’re asking for an MMR reset, that’s completely different. That would be an absolute train wreck. You would have GM players playing with bronze. You’d have Silver and Diamonds in the same game. It would be absolute chaos for at least a month until things settled down and then everyone would pretty much be back to where they are now and nothing would change.
The system we have no is not nearly as broken as you think it is. You just don’t understand it. (Not saying this to be rude). Check out Kawuumba’s post about how ranked MMR, SR, gains and losses and the accuracy of the system ties together. He also includes references to developer responses where appropriate. Nothing is guesswork except where explicitly mentioned.
Also, I have never heard of a single game that did a complete reset of a ladder at the start of a new season. Even Hearthstone doesn’t appear to do that. It takes your previous rank and then drops you down a bit at the start of a new season.
That’s both an easier system to program AND to feel like you’re climbing, but it’s also deceptive because Hearthstone is played 1 on 1 and not 6 on 6. A system like Hearthstone wouldn’t work as well in Overwatch because there are 12 people playing at once rather than 2.
It doesn’t look like League does any kind of reset between seasons. I could be wrong here but a quick look leads me to think otherwise.
HoTS ranked system include a similar reset to OW but the placement matches are weighed more heavily than they are here as the matchmaking restrictions are looser for ‘unranked’ players.
I haven’t bothered to look into Dota 2 or CSGO or anything else as of yet but if you can point me toward a game that does a ‘hard reset’ between each season I would be interested in seeing that as, like I said, I have never seen a game do that before.