This is precisely why I said Bungie should have made a Destiny 3 instead way back when sunsetting in this game was first announced. Of course, people were too shortsighted and immediately disagreed, thinking the franchise would be better without a third game. However, they didn't see what kinds of problems it would pose, like that Bungie has to maintain, test, and update upcoming content for 7 different platforms. Destiny 3 would have at least been a way to renew people's interest in the franchise and not lose the effing vanilla campaign that Destiny 2 launched with— or any other content. I would have rather had a new game than be stuck at the mercy of Bungie deciding which game files— locations, story missions, strikes, etc.— need to go because their infrastructure wasn't designed to hold such a vast amount of content.

Original tiles are considered "too old" to accommodate our movement so they get reworks to fit the gameplay. Solar rails? Seeing the fallout from threads about that and how some big clans putting high tax on playing there, I doubt it will return anytime soon. Original melee system? With melee hitting enemies through walls and just spamming E, I'd say new melee system feels more fluid

Loot variety doesn’t just account for gun model, ect. I was referring to each fire rate being unique with their base stats and how they function. Warframe has a lot of these too, but it’s compounded by part 2 of this statement. Destiny perks tangle up the game a lot. When you have a Messenger with Rapid hit, High-cal, and kill clip you need a base archetype perk for the weapon (high impact boosting stability and accuracy while stationary and/or crouched) rapid hit needs to keep track of you precision hits, and kill clip has 2 timers running after tracking a successful kill. Add on top of that altering the weapon’s flinch factor due to high cal. Warframe AI complexity for base adds is very bare-bones. Most are simple (attack when in line-of sight and within range, throw grenade if target was in sight but now isn’t). D2’s uses that as a base line, but also has dregs flee if you kill too many of their Allie’s near them and you get too close. Hive Knights throwing up their shields if you land too many headshots. Captains teleporting more often when their shield is broken. Not that big of a set up, but it’s one that exists and ties up interactions a lot more. D2’s particle effects come up very often (just shooting an energy or heavy weapon has some). They are a drain on processing power and can affect anything from area lighting to weapon shaders. Warframe has these but they generally aren’t as often. Most of warframes effects come in the form of abilities and enemy fire. Warframe has dedicated servers for PvP only and help the game run much more smoothly in there. Warframe’s a good game, but it’s much more streamlined than Destiny is. Most of the PvE locations are a mish-mash of reskinned hallways and openings. That’s why the open world locations are comparatively much cooler. Warframe has portions that suffer too due to connections, but it’s overall had much fewer complete overhauls that D2 has had in its lifetime. That’s why Bungie should move to make a true D3 on a new system with a fixed up code and invest in some sort of dedicated servers.

The engine is way older than that.

This game engine is from Halo Reach. It was “updated” for Destiny 2.

Updating the engine can only do so much. 75% of the code was built off the old system, Bungie would need to go in a rebuild large portions of the game in the new system to see any real change. I’m sure they did some, but obviously it’s not enough to keep up with how D2’s expanding.