I remember when this situation was brought upfront with GoW Ragnarok trailer (boat animation and look). Then there was no issue, but with AC or ER seems to be.
One of the major criticisms of ER is reused bosses but also reused assets from previous games. Example the asylum demon becoming tree sentinel or the silver knights becoming crucible knights. Why is it bad for developers to take old assets, and repurpose them if it only improves or adds to the content / value of the game for the gamer. In the example of ER many of the main bosses are completely new but the side content utilizes assets from their previous game. It seems like a good way to cut down massively on development time and adds to the berth of content for a game if instead of creating everything from scratch just reusing what was already there. I know this is common sense to most but one of the criticisms of “this is just x from old game” seems like the worst kind of nitpick.
There should be no issue with this, If it helps speed up a games production which these days takes far too long and is only getting longer.. then we should embrace it.
Obviously not overdoing it.