No offence OP but you have the wrong end of the stick here. Let's put it like this:

Fights like Shinryu represent the climax of the expansion. Unless you wish to do the savage version, it is typically a one-fight deal unless you get it via roulette's. As such, the only people who will typically queue for ShinNormal are those reaching the end of the expansion, who often get roulette or mentor queued players in response. In that light, you should understand (some would even say 'expect') that not everyone in a Shinryu Normal is going to be 100% knowledgeable about the fight, or even their own class, and certainly not all will be over-geared. Even those you get via roulette may not have done it enough to remember everything. Such a fight should not be compared to, say, dungeons, which are easier and more frequent by default and much more forgiving. Again, we are talking about a 'last boss' here, not a content-type you are meant to farm or repeat too often outside of Savage, which is a completely different ball-game entirely.

In short, no, I would not be in favour of nerfing it. Even at the time of Stormblood's release when I reached Shinryu pretty early, back when overgearing certainly wasn't a thing and experience was rare, it didn't take long at all to see it through. It's not exactly difficult - it just takes time for those who haven't seen it to get to grips with it, more-so with first-time tanks and first-time healers who are experiencing it blind.