I haven’t play since season 3 or 4.

Game got too easy.

they're slowing the leveling pace. scaling pit tier harder i think. if you played s3,4 and still have no expansion bought then i suggest not to play.

Is the game bad without the new runes system. What are they for?

Grant you access to new power. Basicly some more multipliers or unique power that you can only get from runes. Some top builds this season require rune in order to work. Have a read on rune guide somewhere online. At this point, anyone without access to rune should not be playing imo.

Won't play until they raise level cap

wait for expansion