I would argue that the game isn’t balanced for any level. Nerfs/buffs appear to be more to do with popularity and pandering to various groups than anything else.
For example, if the game were balanced exclusively for gm Ana would have been nuked years ago. Equally, F tier heroes such as Sym would have been buffed to compete.
Moira and Brig were added specifically because the groups you listed screamed that dive heroes couldn’t be nerfed despite dominating the meta. They demanded counters instead and, well, got them 
Overall I’d say the game is deliberately imbalanced to keep various vocal groups happy. Nobody can look at a game where Ashe and Sym both exist and claim there’s even an attempt to balance both of them.