Sad to say but the game has been dying for several seasons. The refusal to remove one-shot assassin meta is because it's "exciting" to watch, and esports/skins are where they make their money. If they balanced the game properly and reduced damage (or increased defense, whatever works) then the pro-play matches would be "less exciting" and less people would watch. That means less money.
It's also the reason (guessing, but likely right) why chromas were introduced, to increase skin sales more by doing less work than making a skin from scratch.
And the removal of TT and permanent addition of TFT is 100% because they can make money off of Little Legends. It's also the reason they don't allow people to buy them individually and have them in groups, so that you spend more money to get the one you want.
In reality they didn't need to do anything with games like Nexus Blitz, TT, Dominion, etc other than bug fix. But these game modes don't produce money and cost money when there is an issue. Is likely what Riot thinks.
Long story short, Riot is following business logic while ignoring good game design logic (which yes does include fun/decent balancing) to make more money because they know that League of Legends is dying and they don't really want to make a full new game that isn't League of Legends (and no TFT is not a new game it still League of Legends).