It used to be there were several places in the MSQ where your character would fall behind in level and you were forced to do a fair amount of side content to catch up in level before you could continue. They made adjustments to the MSQ so only XP from the MSQ should be needed to keep up in level. Unfortunately, XP bonuses available have tended to swing the problem in the other direction now.

You mentioned a couple of things I've brought up before on how it negatively impacts the leveling experience. I'd honestly like to see the XP bonuses disabled if the active job is at or above the level of MSQ progression because there is zero benefit to being overleveled if you can't access higher level side content. It won't completely stop the overleveling but it will slow it down quite a bit. One to two levels higher doesn't unbalance the leveling experience like being 15 levels higher does.

One thing I've learned to do when leveling a new character is to unlock additional jobs and switch between them as I play through the MSQ. Right now I've got one character that's NIN/WHM. I use NIN for playing through the solo content then switch to WHM when it's time for a dungeon/trial for the faster queue. That helps to soak up the additional XP. The one physical damage and one magical damage job combination works well because the MSQ alternates between the two types when giving gear rewards until you reach Shadowbringers content. By then XP gained compared to XP needed to level will have slowed down considerably and you'll probably find yourself ready to focus on a single job until you've reached level cap.