I believe the closest you can get to "objective" balancing is based on three factors.
1. Ease of Use - how easy it is to use the class, how punishing failures to execute rotation are, how much "effort" is required to hit maximum dps.
2. Utility - what does it bring the rest of the party? How much rdps/mitigation/heal does it bring?
3. Mobility - How much can they ignore mechanics and/or move with a fight and how punished are they for doing so. Essentially how difficult is it for them to "Adjust" to mechanics.
I believe the key factor in MCH's balance is that in 3, mobility, they can pretty much ignore any/all mechanics for ease of movement and are not punished at all for placement. As someone who loves MCH dearly it's the "Easiest" class in the game imo to play. I don't have to worry about up time, I don't have to worry about movement, I don't have to worry about buffs, and aside from a bit of burst damage I can pretty much stay in the top 1-3 in most content just loosely following the opener.
The issue here is how do they balance this ease of use to make it not punish other players, and it's an issue I believe they've had a while (see my previous main, NIN).
If you buff MCH to be able to do like high end melee/SAM/BLM numbers of damage you create a class that can easily hit like a truck with no punishment and literally no tactical thinking involved. No optimization of uptime and aside from maybe server ping no real drawbacks.
If you give them more utility it starts to copy BRD and DNC (See BRD in SHB having this same problem because DNC took most its utility/role in the group).
How fair would it be to have them do as much damage as classes that have to move around AOEs, utilize uptime, plan out their rotations/burst, etc. I've seen on the forums before that people believe mobility shouldn't affect dps balancing but I argue that it is probably the biggest reason why MCH is stuck in the weird limbo it's in currently. Perhaps the cast time while moving introduced in PVP could introduce a new skill/capstone next expac that allows for movement (slowed) but dps to provide more "skill ceiling" to the class or they could give it another personal dps buff it has to set up.
As someone who mains NIN and watched RPR come in and do way more damage, with my utility on a single button press, and just top dps for a while, I feel the pain of watching a class you like kinda become negligible, but I also believe the dps checks in this game aren't bad enough to warrant "needing" a specific comp if you don't eat aoes.