You see the entire reason devs stick to the same engine despite issues is because it lets them create content faster than they could if they were to start learning a new engine and modifying it to their liking. This is why Bethesda is still using that engine and not fixing it despite it being possible (if it wasn't possible all those unofficial mods wouldn't exist, and Bethesda has never hired anyone to look into those to implement it officially in the engine).
But Destiny already has issue with slow content creation, any slowdowns and additional cost caused from getting used to a different engine and modifying it would likely be less than the slowdown their current engine causes, ofcourse I'm only guessing but we have Destiny's content drop frequency and size to use as evidence. And this is not something new as this engine issue causing development trouble goes all the way back to Halo 2.....15 years ago ! They did say they improved it in D2 but it doesn't really seem to matter much as the output seems to be barely better, and whether that slightly better output is due to the improvements or whether it's due to help from other studios....I don't know. But they do need restructuring and a change in their development philosophy desperately.
