I don't want to suggest changes as big as DBM like tools cant effect the culture but given how SE designs content, as you point out- I feel, personally, that even if it was sanctioned allowed... it wouldn't be as substantial. Though I respect you feel differently.
The fun part of don't ask don't tell (/s lol). I'm not particularly against addons, as I actually loved them in WoW even when they were annoying due to a patch (but that was in part because Blizzard didn't really care to ensure things worked). I understand some concerns are placed upon them, some of which I can vaguely understand and some of which I feel are stretched. I believe having a publicly allowed parser can do things like it did in WoW, but I don't really believe a private, allowed, would cause many if any issues. Some people may ask to see your parse, which you could simply lie or tell them to go get Thal'd lol. Though similarly I respect the concern, and community management is something difficult to get back on track once you feel you've lost it.. so... conservative approach isn't mystifying.
I think you agree with me but maybe disagree on wording. Because what I meant is that, like a baby sitter raid leader, the tool will keep you hyper informed. GET OUT OF LAVA, STAND IN CIRCLE, GO TO "X" PLAYER. This to me is called awareness, now you might like it if I called it artificial awareness since it wasn't a skill provided by the player but rather by a parrot shouting mechanics.. but functionally it's still awareness.
As such if a player is more aware, whether naturally or artificially, this has an impact on play ability. Such that I would argue on a aggregate whole such tools have a direct impact in the ability of players and thus allow them to perform better more consistently while using less personal stress / skills. For me in WoW for example I found the tool helpful to casually enjoy harder content, as I can easily follow instructions but I just don't want to memorize the fights lol. Having used the DBM type stuff in WoW (another one existed back then too) I would argue it was a direct impact on my ability to output high performance while also feeling less challenged at the same time. Naturally this impacts perception for both players and developers. "This content is easy" says the player with the professional never wrong parrot- silly statement, and may cause damage to players who don't use the tool (and likely annoyance to the devs). Also messes with statistics and expectations devs have of players. Then again I feel given SE tests their own content, to which I assume, without tools I think they have significantly dampened the damage from the situation and such I am less worried about it and don't care. If someone uses to have a more stress free / easy experience then whatever. In most situations I don't care if someone made it a bit easier in such a way, though I can see how doing it for the hardest content in the game as a race of skill is quite upsetting.
Personally I don't think being aggressive on banning will help much on the situation, particularly if they don't scan the PCs (in that case, pretty much just hot air even if they punish a few streamers), but I do think adding the things players think are useful without damaging intended gameplay is a smart alleviation to dissuade more people from feeling the need to use the third party tools. Also may consider adding an official framework to which you could have even more control over the situation, but /shrug. The whole situation will feel like variations of losing no matter what lol. I've been okay with the don't ask don't tell type policy but certainly I see ultimate's can make that more frustrating for those who want to show off their talents (particularly speaking ultimate, as otherwise I generally think people playing how they want is fine so long as it's not like toggle god mode or infinite gil hacks lol).