Job difficulty is irrelevant and SQEX said they wouldn't balanced on job difficulty.
How about difficulty of maintaining uptime?

It's only fine seen from the outside, because it works. What's the point of buying a faster car that will get you to your destination in 2 days when you have 3 free days?
But now imagine the faster car also had extra feature like air conditionner or GPS? For the sake of simplicity, we'll say both cars are at the same price.
Yeah things don't work like that in the real world. Applying that analogy to the game, if you care that much about killing a boss a few seconds faster vs playing a job you enjoy then by all means feel free to switch every balance patch. It's never going to be perfect, there's always going to be someone on top and on bottom. But yes, it works.

you want to balance around casuals that only run dungeons, use bio blaster on a single target? Skips cooldowns and sometimes even forgets their dots?
You'd have a terribly unbalanced game if you ever did that. Some job would be useless, others completely broken.
OP posted an example of the best players in the world, you're listing an example of some of the worst. There's a whoooole lot of people in between those two examples and a lot of them don't even log, the average player is somewhere in there and that's probably what they're balancing around (I would guess). You can't balance for 100th percentile parses and expect everyone to play at ultra top tier.

Ya'll are making assumptions off a small amount of data like it's the end of the world. The people who bother to upload logs are likely to be better than most, we're missing a lot of data.

Idk what kind of data they use at SE or how they aim to balance their jobs, if we were privy to that information we probably wouldn't need this discussion. Alas, here we are.