I think the ranked reset is necessary but is poorly done.
Full disclosure:
That's my opinion from what I've read and before I've experienced it myself - last season was my first season of ranked (promoted to gold 5 thanks to around an 80% win rate over my last 20 games or so) and i won't be doing placements for another few weeks at least.
Anyways, here's what i know:
Maximum reset rank is platinum 1 - people in diamond to challenger are all grouped to the same level, which is ridiculous.
It's possible to go 10-0 in placements (or frankly even 6-4) and end up at bronze 5. Given the "reset" should bring people towards the average, anyone below silver towards silver 5 or 4 should theoretically improve. If your mmr is so low you're guaranteed bronze 5 it should just say that and let that 9-1 record get you promoted to bronze 4.
People don't know their mmr and don't understand what's happening behind the scenes during the reset. Riot doesn't need to share everything, but it could be a lot better. At the end of your placements Riot could show the player: you were ranked X before the reset, your mmr was (below / approximately at / above ) this rank. The reset gave your previous rank (y% to y+10%) credibility. You started placements at rank Z and then show what rank you were considered after each match.
E.g. for myself (theoretical, i haven't played any games)
Finished rank gold 5
Were approximately at this mmr
You played 68 ranked games so your history received only 40-50% credibility.
Reset brought you to rank silver 2.
Game 1 - win, silver 2
Game 2 - win, silver 1
Game 3 - win, silver 1
Game 4 - loss, silver 1
Game 5 - win, silver 1
Game 6- win, gold 5
Game 7 - loss, silver 1
Game 8 - win, silver 1
Game 9 - win, gold 5
Game 10 - loss, placed silver 1 out of placements.
So instead of going 7-3 in placements and feeling cheated being at silver 1 0LP, since i had been gold 5 and thought i had gold 3 mmr and did well in placements, i instead understand how i ended up at silver 1 and can clearly see that i could have placed in gold 5 but lost some key games (never won a game when at gold 5).
I think riot would still have their secret system but players would understand how it all worked really clearly.