The phone 2 processor is a beast but 2 years back.it is made with a power of only supporting up to 60 FPS in high-end games (as claimed even it struggle to maintain 60fps) Snapdragons latest processor 8gen 3 which support 120 FPS in pubg(till now 90fps in bgmi) also struggle to maintain 90fps constantly.even after knowing that this processor is not capable of 90fps ,the top brands to make there market forced this chipset and bgmi to implement 90fps.
In TBM(small maps needs less performance)the fps are like 85 to 89.9 .
But in big matches like arengl map the fps are normally 82 to 89 :- when there is no rush,the FPS drop to 65 to 80 when there is intence fight,when a mejor of players appear in asame please.
So donโt think to much,the processor is trying its best ,the performance can be increased by increasing the maximum clockspeed of the the chipset(like in iqoo neo 7pro) but it will lead to overheating problems and that will be a even big issue.