Its true that there will always be people complaining about anything in the game - and obviously its also true that people complained about previous relic steps/grinds.
However there are two types of complains here:
(1) Complaining about the grind
(2) Complaining about the content (involved in the grind)
The first type of complaint is the one we saw with basically every relic, from Atma to Pagos. Depending on the actual time required and the RNG involved (...Atmas...) I consider those complains to be more or less legit. Most of them "less" legit, to be honest.
Now the second type of complaint - thats the one we're seeing mostly when it comes to Pagos, but didnt saw so much when it came to the other relic steps. People complained about the RNG and having to run Lost City 50 times to get their drop, but they didnt complain about Lost City itself. With Pagos (and Anemos before, even though Pagos seems to be a lot worse) I dont see so many complains about "This takes to long" but rather "Its not fun getting there in the first place."
And that is the issue here - not the grind, that was the complaint of former relics, but the content itself. The core of this relic-grind - Eureka - is rotten and not fun. The core of former relic grinds had the advantage that it consisted of several different types of things to do (so if you didnt like one of them, there was at least something else for you) and that those different types of content worked better by itself.
A lot of the content involved in old relics were dungeons and trials - content that works well with FFXIV and its combat system, because it has mechanics and is engaging that way. I dare say that most people like dungeons, because I cant really imagine how someone would decide to (continue to) play this game if they dont.
Eureka however works against the strengths of the game - less mechanics, more focus on a combat system that by itself isnt that enganging.
Tying the weapons to Eureka only also means that there is overall less variety - in mechanics, in types of content you do, down to simple things like area, atmosphere and music. The Atma-grind was aweful, but at least I could freely pick the scenery and if I got bored after two hours in the desert, I can go into the forest. During the dungeon-drop-grind in ARR I can switch between different dungeons, musics and atmospheres - and on top of that all of them are more or less good content at their "core".
I would agree on ignoring complaints about stuff being to grindy - complaints about "This content is not fun" should be taken serious though.
I got the impression that most people disliking Eureka dont mind the grind, I can say about myself that thats not the issue I have with it. The issue is that the grind is all about excatly one type of just not entertaining content.