Let's be honest. There are really only two "strategies" for end game content. You can melee zerg it or you can magic burst it. Some mobs respond better to physical damage while others respond better to magic damage (or are just to dangerous with aoe to try physical damage). The rest of the fight is learning the mobs gimmicks. So if you are arranging a PUG to fight a particular mob you need to first learn is it better to melee or magic. Then figure out its gimmick and make sure you have a job (or jobs) that can exploit/minimize/etc the gimmick. That's how you build a party for every single Escha zone mob. Some of the gimmicks can be annoying to deal with but most can be addressed by adding one or two different jobs (like smn or cor for Caturae fights). If I am doing a new fight and I can't find anything on the wiki (which is really rare) or a video (which is even rarer) I ask my linkshells (you can have 2 on at once) and usually someone has done the fight before and knows the gimmicks. Also remember that HP in Escha scales with party members so if you go in with 10 people you will have a harder fight than if you only had 4 or 5 (trusts don't count).

Lastly, don't forgert vorseals. When I first came back and was trying to solo the Reisenjiima portions of RoV quests, I was missing just about every hit. Without significant upgrades to my PUP gear, but just completing content and the dragon fights, I now hit most of time. Quetz provides an accuracy bonus that can be upgraded based on the number of times you've fought and killed him. The higher end requirements are kind of insane, but there is no reason you can't have the lower tiers done. Sure Quetz will probably kill you, but so long as you contributed in some way to the fight, Quetz dies, and you don't HP before he dies, you get credit for the fight. If you aren't jumping on every single Quetz fight, then you are leaving free acc on the table.