It depends on a lot of factors. If you just do MSQ, you will get just enough experience for one job, maybe slightly less than you need because some levels used to expect fates and sidequests to be done. SE has tried to remove those requirements but they might still be needed for some levels.

If you do sidequests in the latest expansion areas, you will get enough experience to level multiple jobs because this was the first MSQ designed to not require sidequests in the first place.

If you have a lot of experience buffs, such as your FC "Heat of Battle" buff, food, rings and earrings from certain locations, you might get enough experience from dungeons to outlevel the MSQ. If you do roulettes every single day, you will definitely outlevel the MSQ. If you have the Preferred World bonus "Road to 80" buff, it will double quest experience which will keep you, on average, twice the level of the MSQ or higher.

I know you don't want to be told "play your way", but switching class all the time is annoying and causes mental fatigue. It's easier to just do the MSQ on your main class even if you get to max level and don't receive anymore experience, because getting experience is easy in this game and it's increased for alt classes.