I agree with this 100%
It's like WHM and AST are analogy for running and walking. if you walk, you get to your destination slower but safer, and with less exertion or fatigue. When you run, you get to your destination faster, but you risk injury, exertion, fatigue, and possible filthiness as the trade off. however, WHM is walking and getting there faster than AST who is running and putting in more effort. there is nothing subjective about walking and running as running inherently requires more of you than walking. in this case, the job with more targetted abilities and a rng defined rotation in it's horrendous card system and a weaker healing kit as well as, a weaker Mp contraints is OBJECTIVELY harder than a job with the best healer MP management, strongest healing kit, no targetted rng mechanics and whos sole optimization stems from hitting Glare, or giving up 3 of them to use Afflatus Misery. we can sit here and act like just because most of the jobs are close in difficulty, difficulty shouldn't matter. But the difficulty between AST and WHM isn't a small one and those who don't play them both will hold this half hearted stance that difficulty is 100% subjective for all jobs.
You're partially correct, it is largely subjective, but not completely subjective. the idea that some jobs are more complex than others is just as true as the idea that difficulty is subjective and as a result, you have to be objective when looking at the kit of both jobs while paying attention to the communities discussion regarding said kits. jobs that are difficult usually seem outcry which we see with AST and it's card system as opposed to WHM, where we don't see this. there aren't any post with someone complaining about the difficulty of the job in any part of it's kit.