TL;DR: You're probably fine to proceed as a Tank, especially since you do the research beforehand to make sure you know your specific mechanics for an encounter.

In FFXIV, no dungeon bosses are skippable and skippable groups of monsters are rare enough in the late game to evoke images of unicorns. You'll find skippable monsters primarily in the dungeons you use to level up to 50, and as long as you're the Tank people are less likely to complain about full clearing a dungeon because doing so will earn more EXP. If people get mad at you when you haven't made some sort of mistake, they're probably in the wrong. Just shrug it off and keep going. Contrary to popular belief, many runs go quite smoothly. The bad ones just seem more prevalent because that's all people ever pipe up about!