I do feel that when people start comparing jobs or roles, they tend to focus on specific facets without keeping in mind that difficulty for any dps job tends to spread across multiple sides. As a result we often end up with wildly spread memes about ranged physical dps being the easiest in everything, BLM being the galaxybrain job, etc.
In my view there is at least 3 main elements that constitute the challenging aspects of any given job on the DPS roster (support jobs would have different metrics due to their support responsibilities):
- Role constraints: range, which introduces melee/gcd uptime, and cast times, which introduce casting/gcd uptime as well, and a secondary constraint being positionals on melees (which can increase dps slightly if met).
- Rotational complexity: essentially how intricate, deep and complex a rotation can be. This includes non intuitive concepts (old formless on monk, astral fire / umbral ice mechanics on blm, etc), but also finicky jank in optimizing a rotation (bard song timings), or just how complicated a rotation can be in terms of moving elements and/or choices to make at any given time where for example a proc based rotation is going to require more constant brain uptime to upkeep than a fully deterministic one.
- Busyness and APM. This is often overlooked but having an extremely busy rotation will take a non trivial part of attention and upkeep from the player in comparison to a very slow moving rotation.
- Not to be necessarily included into a job's difficulty to play so I'm keeping it apart, but there is still the important factor of accessibility and skill floor. Most jobs are accessible those days though, but it should not be overlooked on why certain jobs have been considered enigmas by many new players or casual players.
As such, if one takes for example BLM, then on 1) it is rating high in difficulty and this introduces a lot of planning ahead of the script notably for challenging content, just because it's not a mobile job due to being a true caster. On 2) however, it rates relatively low once people are past the initial obscurity of some of the job's core mechanics: the rotation is a very simple loop in theory and the difficulty of the job relies in upkeeping it in relation to the first point (unless people start going very deep into non standard). On 3), it's also extremely low, due to being a caster: very little weaving or OGCD spamm, not a lot of buttons to press all the time which gives some time to consider moves.
It's possible to do the same for every job in existence, VPR being above average on 1) due to being a melee with range and positional constraints, rates relatively low on 2) with a rotation laser focused on fewer buttons and moving parts, but rates very high on 3) by its sheer APM which leaves very little breathing room when playing it.
And then you can rate SMN "very easy" on the 3 points because that's SMN now.
Personally that's how I go about rating jobs and roles, that's also why I'm always a little uneasy when I read how this or this role is way harder to play than another for X or Y reasons. Obviously, the most important factor to always keep in mind is that difficulty no matter what, is extremely subjective.