the double TP meta WAS the tank meta because as we all know, tanks are immobile and do not farm as well as other classes
the marksmen updates occurred in preseason 6 and season 6, effectively just 6 because they pushed the mastery update at the same time as the marksmen class update. This is conveniently after all of their previous balancing decisions started to get ignored (and also conveniently when Tencent bought out Riot's shares in the company for 100% total ownership)
i'm not sure what you mean by siege meta...waveclear has ALWAYS been important but it rarely eclipsed other strategies and it was usually MARKSMEN and ADCarries that did it the best
Do you remember when you did not have to worry about picking an immobile character or a non-meta character?
that's how good things were in early-mid 5 and previous seasons. Most niche cases of balance issues didn't last for 6 months at a time like the current seasons do, then late 5 and later seasons came around and suddenly Lee sin could dominate the jungle for the entire year, previously toxic strategies got put BACK INTO THE GAME, most strategic elements have been removed or heavily modified in favor of DEATHBALL TEAMFIGHTS, lategame is now achieved at 2 to 3 items...really, things put into the game TO PREVENT SNOWBALLLING actually INCREASED SNOWBALLING
Off-meta debates(which spark way too much discussion and also show how at risk everyone is)
unhealthy wide-spread changes (runes reforged, multiple jungle updates per season, true damage on everything, replacing problematic elements by just switching them onto another item...etc)
things went downhill and snowballed out of control...ironic