Currently in 4.x the 'BiS' is more straight forward as you have to look at your DH and Crit value as a combination, since there's no "accuracy" anymore in the traditional sense. For example, a combined 3300+ is seen as the baseline. Is it the best? Course not, but that generally means you at least use the crafted gear, which again for a job like BRD, for example, outside of Savage is again BiS in some slots, but that means 4.2 you'll likely be rocking the crafted gear from 4.0 if you didn't touch savage.
Every even patch is almost always a reset where people who actually do content will simply just have a headstart compared to people starting from the ground up that didn't touch content. So while I wouldn't say it's "personal", it's just simply easier to understand because of how some jobs play differently where you don't have to have 710 accuracy for example but rather a set value DH/Crit. Healers for example only need to have a DH value shown on their stats in order to DH when they DPS, so they don't have to focus on it as Cures don't miss or have accuracy attached.
In terms of downing fights, you have to start working towards the 'BiS' if you want to REASONABLY down Omega 3, 4 and the upcoming Shinryu Ex (based on Ilvl gear it drops) and Ultimate Coil. You can do it without, sure but constantly hitting enrage or JUST about to as it dies means there's slack somewhere. It's not a bad thing but they're designing content on such a low end scale with the exception of Omega 4 that it doesn't matter as much as 3.x where you NEEDED to maximize every aspect of your gameplay. It's very easy to do but you still have people who shrug off a tiny challenge, e.g people who are too scared to touch Lakshmi/Susano Ex despite being the easiest set of primals to exist in XIV that didn't come from the previous version.
The reason composition changes values is because BRD is actually a support now, so directly controlling people's Crit and Direct Hit will influence the raid DPS greatly, ontop of how absolutely RNG brd's DPS is as well will change "BiS" because there's no gear that can influence proc rates, because Yoshida is scared people would "alienate" someone who didn't have xyz gear like other MMOs, when ironically if you don't personally hide your Logs on FFlogs, people on the NA DC will use that as a measure of your skill and auto kick you if you don't have the performance to their liking, as if you read reddit for awhile people were getting kicked after joining a party at seemingly random, but it's because they were in a party with someone who uploaded the raid log and their DPS was substandard.
So the 'meta' is the same as 3.x, just a lot easier to understand and they're pacing gear better this patch. It depends on what they decide to do with 4.2 if the concept of "BiS" is truly thrown out the window.