What change do you want to see on your main class for Endwalker ?

[CKNovel]

The two Jobs that have the most issues in the game are probably Black Mage and Summoner. It has nothing to do with the End Game experience on them, because I think both are fairly good. Black Mage is just rough because what defines a caster is the casting timer, and it's the poster child of the entire caster lineup so it has some of the most outrageously big cast timers of any job. What makes those two problematic is that what they do changes a lot from low level to high level, making level sync a problem.

We can basically judge what is at the gold standard by what jobs are keeping the same rotation as they level up and just adding things to them. So stuff like Machinist actually is at gold standard. Dark Knight is another job at Gold Standard, and I believe the four jobs they introduced in the last two expansions are at gold standard. The ones that are problematic are ARR and HW. You can't really learn a job if the job doesn't even give you the right rotation until level 70 or 72. Paladin is kind of iffy on their rotation and I think they are definitely doing some tweaks to it come End Walker.

Wrong, if it was true you'd get the whole rotation from lv50.
The leveling experience only serves to learn the basics, each time you get a new skills, it's like another note added to a song. Leveling only serves as progressively learn your job until you reach the cap where you have all the tools to complete your learning. SMN is a mess, that's true and BLM is for sure completely different between 70 and 80 as most of the skills learned are QoLs.
What's the point of balancing jobs during leveling when a player will spend at most 1 hour until a new skill is added? Leveling is a tutorial to the job basic, it's pointless to balance and design around job leveling.

Your rotation will evolve in any cases as Dungeons are mostly trash group followed by a boss, starting with some resources.
Use MCH as an example, your "gold" standard. Auto-Cross Bow and Bio-Blaster are far more usefull in these scenarios but won't be seen in endgame content with a single target, which is more than 90% of the played game.