I played alot of mmorpgs and met a lot of ppl in there. I actually really like addons since no game can hit all tastes in terms of UI-Design and stuff like that. For example, my brothers interface looks like dimensions different to mine, not only in position and scaling, but also in colours etc.
Since Im not a developer and have no clue about the vulnarability you get by implementing addons (bots, hackers etc.) I actually dont care to much how you decide at the end, but for me, the most important thing beside a huge possibility to move and change your UI is the Dmg/Heal meters.
In my eyes all "alternatives" to check your dps was just bad. It kills the complete competetive aspect of an mmorpg if you cant track detailed numbers. For me as a min-maxer its really important. For those, who say "dmg meter brings toxic behaviour" is just bullshit. For example "New World" has by far one of the most toxic communitys. Theres just a small part of ppl who kick someone because he is "low on dps" or insult him. Toxic ppl always find a way to flame, they dont need an dps meter for this. Also the DPS meter exists since 2004/5 in WoW and theres still ppl dont using it cause they dont care. So for me, its just the most important thing to use one, since the "theory" behind some specs is also a huge and interesting part in mmos. Its also more transparant to fix / balance classes.