A Destiny 3 is the last thing most people want, but a Destiny 3 gets them off of their dated engine (if they were smart devs -blam!- there was an issue) and also got them to reinvest in their network infra. Most of the issues with menu load times is that Bungie isn't properly using caching and memos for their menu or items in it so you get long loading times while they live-fetch the information needed. For instance, you wanna check your rolls on the guns you have equipped: You load your inventory, the entire inventory is blank with loading icons, you get that to load, then you inspect your primary, it's loading the texture, model and perks (even tho you already saw the equipped perks on the previous screen) and the mod, masterwork and shader. Anytime you switch screens it's doing a new live-fetch for information. Memoizing the information would be more efficient and fix the issue of long load times in your inventory unless it was a new item. And then they could cache frequently used information during runtime like say you're loading into the tower, when you load in the game could cache Gambit, Crucible and Vanguard inventories since they are generally static and don't change over the course of the season outside of maybe the switch from Seasonal Gun, to ornament to Exotic and upgrade materials.

It's one part "needs new engine" but it's also many more parts "needs new server architecture". The game engine itself could be upgraded, but that's more client-side features like DX12 / Vulkan API and Asset quality. D2 was made on D1's tech. So great start, a 2017 game made on 2014 tech... honestly that's fine, but now we're going into 2023 and playing on 10-year old tech. Bad situation. Beyond Light made "optimizations" to that tech, but the base hardware / architecture was still the same. Higher enemy density activities is one easily found benefit. 7 year old architecture at that point. It -sounds- like there is a server update coming with Lightfall. I mean, there has to be. If the current level of content NOW with the current playerbase level is causing the servers to suffer, how the crap are they going to maintain their "No more vaulting" stance?