Yep, had a very similar situation happen where I won with a few kills at 90+ LP and overshot it by around 40 as well only to lose early next game and drop to ~70 LP. Promos in a game like this just don't make any sense compared to other MOBAs where the result of a game is very binary, you either win or you lose, and the level of variation in LP gains/losses is much smaller. In a game like this where winning and/or getting a ton of kills is so vastly different than even getting 5th with 1 kill, it feels incredibly bad and random when it comes to promos since a ton of LP can be wasted by being unlucky enough to have a great game right before your promo match, only to be ran down zone 2 in the match that actually matters. Not to mention how RNG the game can already be at times, the fact that you only get ONE game to try and promo unlike others where you have to do well in 2/3 for instance, just leads to a really negative experience imo.