Warning this may be messy but i try to predict and solve different scenarios i faced before
if you're new to whole " PC Masterace " ( which is also a bulsh*t ) you should know that the whole " Minimum " and " recommended " requirements are bullsh*t, in fact, having older/worse hardware may give you better result than " powerful "
because bungie decided to disable On-Screen Displays, its harder to test things, but if you have software such as MSI Afterburner, EVGA precision you have option to monitor your hardware ( GPU temps, usage, Vram usage, CPU temps etc ) now because you cant have them on screen you have to alt tab ( sometimes causes crashes or give worse fps spikes ****but because you already have one, why not get more?**** ) ( also in settings you would have to tick and enable them to check: GPU Usage, GPU Temp, Vram Usage ( GPU Memory ) CPU Temp, CPU Usage, optionally CPU Clocks, Ram Usage ) usually the spikes or ( Frame drops ) occurs when hardware chokes and cant handle the instruction, or run slower than usually ( usually due to throttling ( having to decrease its clocks to keep the temperature is safe area and to protect it self from being damaged / broken ) or even if you are above your GPU VRam limit ( eg lets say your is 8GB and you're running at 12GB, this means that the GPU Memery doesnt have enough space to hold your the textures and has to " lag " to get them and dont break the "view" and sometimes its your RAM ( Physical one ), if you monitored them and see that nothing stands out ( on graph there is no spike hills or aint running at its limit ) it may not be the Hardware problem but software like game or even operating system ( for temps go check the manufacturer website to see what are the safe temps, but if it runs between 40-60c ( everyone says differently but the key point is that it should never run close to 100c unless its a gpu with blow-style cooler, or a hungry power component ) its good ( also make sure in BIOS you running X.M.P ( Extreme Memory Profile, in short you buy DDR4 3200Mhz but if you stick in Motherboard it runs only at 2133MHz stock speed, unless you select the X.M.P ( there are many different profiles, make sure you apply the one which gives the most MHz ) if you overclocked your hardware ( GPU,CPU,RAM ) sometimes it gives worse results even if it doesnt bluescreen/crashes, if you overclocked revert it stock and test, also dont run games at 4K native or scaled unless you have GPU that can handle that thing, if you running on SLI / CrossFire make sure you turn it on in games settings / change in Graphic Card Drivers ( for Nvidia: Nvidia Control Panel for AMD: AMD ( something ) ) sometimes not running games at SLI/CrossFire gives better results, if you have Integrated GPU make sure the game uses your dedicated GPU rather than Integrated ( usually this option is in game options or in GPU Driver ( Nvidia Control Panel for Nvidia and AMD ( something ) for AMD
from what i expierence is that the Steam version of the game runs worse than it used on Battle.net but what you can try are simple stuff like disable softwares you dont use ( e.g Discord/Web Browser/ whatever you will not use during playing ) sometimes disabling antivirus help ( why would you? first of all antiviruses use resources like RAM and CPU, and these 2 also come in play when it comes to gaming, and sometimes your antivirus software decides to scan your hard drive, this will cause more stutter, also the Operating system matter, from what i know and heard is that Windows 10 1709 gives the best results when it comes to gaming ( Sometimes running Steam with -no-browser and disabled steam overlay helps improve the frame rate )