[Baertram]

About your request:
There is no API givent o show the POI of the dungeons on the map, you'd need to hardcode a list of these dungeon POIs, zones.
Afaik the "wayshrines of the dungeons" cannot be used for that "show on map" and ZOs does not have the data, else their own shown on map would work already. So this would be a list of dungeons you need to update with each patch again.


Just for clarification:
I often read that addons slow down the game and that's not always true. I mean ys additional software makes it slwer but most of the time it's not human noticable at all.

Addons only slow your game down, in terms of loading times e.g., as they use SavedVariables and store a big amount of data. BMU does not do that so it's not slowdown addon at all, only working as you open the map or show the BMU UI.

Or combat related addons or addons related to things like th group UI, and ability bars where each change/usage of a skill or your or any other group menber's attribute values would need re calculation of things.

Or map related stuff that needs to update as the map udates (Cyrodiil e.g.). But even then it uses events that only fire as the change happens, and you'd be fine and not notice and big performance loss.

Or they might slow your game down on very old hardware or low power CPUs which already struggle to provide a good and fluent game play.
In this case I would not add more to calculate and do, like addons, yes.

From what I noticed and know, addons that just add things to crafting tables, or the map, or the UI (and is not based on the above mentioned things) are nothing that really slow down your game. The size of the SavedVariable files in total is what raises the laoding time at each login/reloadui/zone change. And the amount of players in your instance (what we obviously cannot control beside not porting to crowded areas during prime time e.g.).