I do game quite a bit on the mate 9.
Mainly Hearthstone, GTA Series and PSP Emu.
I don't touch the mobage stuffs etc.
I find the battery last a lot longer vs my old S6edge.
And it doesn't get really hot. Perhaps it's the rugged armor?
Display wise, yes, Samsung is slightly better, but I don't miss it nor does it detracts me from enjoying the games.
The only time the display gets really hot for me is when I am trying to use the phone outdoor during noon time when the sun is directly overhead. The display will get really hot because the brightness is bummed up all the way and the heat of the sun makes it worst. But, it's the same with any other phones I've used.