The problem is that it assumes that the devs care about job balance, game feel, or really any aspect about the jobs at all at anything but max level. Just off the top of my head Black Mage at level 50 is pretty weak all around because it's balanced around Fire IV and Flare spam as its damage sources but all it has for single target are Fire and Fire III which are balanced as being Buff Upkeep skills, and it can't Flare Spam for AOE until the 60s. Dragoon is another example at 60 because Blood of the Dragon's duration is balanced around having two combo finishers to extend it so it feels wonky. Monk suffers at 50 from not having formshift in basically all content and a long cooldown on PB that might make sense at level 80 but just hamstrings it at 50 if the boss jumps too frequently (see Titan Hard). Pretty much all ARR jobs are weaker at low levels than Stormblood/Shadowbringers jobs because of 4/5.0 jobs have extremely powerful single target and AOE actions at low levels while similar actions aren't given to those jobs until way later.
Like you say that this is breaking the game balance at lower levels, but the balance at low levels is about what you'd expect from a three legged stool.
