Well you pretty well said it yourself Ambient temps are high summer, and you haven't taking measures to keep your cooling system clean. Your CPU will throttle at 100C to protect it self. 85C to 90C under heavy load for short periods of time shouldn't be a problem, if it's staying at them temp for longer periods I think it will shorten the life of your notebook. First thing would be to see if you can get the dust and crud out of your cooling system.
You haven't listed what your ambient temps actually are My G752VY in Ambient Temp 25.5 C my system Idles at 36C to 38C light Medium use brings it up to 50 - 60 C range and heavy use will top on in the low 70's. I don't game so I can't comment about the loads with each game or any game.
G752VY-DH72 Win 10 Pro
512 GB M.2 Samsung 960 Pro
1 TB Samsung 850 pro 2.5 format
980m GTX 4 GB
32GB DDR 4 Standard RAM
Z97 PRO WiFi I7 4790K
Windows 10 Pro
Z97 -A
Windows 10 Pro