Your issue is not related to GPU utilization and more with your CPU. Ryzen is great and all, but Destiny likes high clocks with low memory latency for it's rendering pipeline and that is two things that the Zen architecture is not great at. There was an improvement with Zen2, better memory controller and higher IPC, but your 2700x with an all-core boost aroung 4.0ghz is just not enough to handle all the draw calls necessary to get higher fps, for that you would need a intel CPU, like the 9700k or 9900k. FYI, before being called a intel shill, i'm using a 3700x, getting around 90~180fps with a gtx 1070. Intel just can't beat the price.

Destiny 2 overheats my GPU's memory. I've had to RMA mine multiple times. Are you sure you want to stress out your card? Lower your resolution. I was playing D2 on lowest settings while using a GTX 550 Ti at 60 FPS and still top fragging. You can safely squeeze out more performance that way. Hell, my friends and I used to play CSGO at 4:3 800x600 resolution for the width and extra frames.

Also why do you need the highest FPS possible you are just burning out your card faster. If you want to ask how to max your 1080 out faster then just go to the nvidia forums.

I'd start by completely uninstalling the GPU driver with a program called Display Driver Uninstaller by Wagnardsoft. Then, I'd manually install driver version 431.60 or 431.70. After Nvidias last 2 drivers, my average D2 fps went down quite a bit. As far as forcing you GPU to utilize itself to 100%, there's nothing really you can do. The game itself, and the driver is what demands performance out of your GPU. I doubt the normal non ti version of the 1080 is going to hit 144fps on average. I'd guess anywhere between 90 and 120 in open areas and 10 to 20% more in closed areas like Lost Sectors and Crucible maps. There's always overclocking, but it's seriously overrated for the minimal gains you get. Not worth the extra heat in my opinion. My 1660ti system and my RTX 2070 Super system get the same fps in D2 where the 2070 is about 50% better in most other games. I'd set D2 up to look the best it can and not worry about the fps too much.

a few things, your GPU will never hit 100% usage if your CPU (Or RAM) is bottlenecking it, im not calling out the CPU im just stating maybe something is wrong there due to the fact D2 hasnt really had a great track record on Ryzen. Secondly, do not run this game windowed fullscreen, Push the resolution scale to the max, turn off Vsync and any FPS cap. I also wanna state that Overlays for other apps can cap framerate, so trying to use OBS or Discord overlay with D2 can also chip at the framerate. I usually get 220-240 FPS on my setup I run an i9 9900k and a GTX 1070SC, now what i believe maybe the biggest factor to my framerate is i run my 32GB DDR4 at 4133 mhz with intel XMP just because Destiny barely uses 2.6GB of my 8GB of Vram.