Your DM is wrong, or houseruling

If the claim is that there is an official rule that prevents you from persisting things with a maximum duration, he is incorrect. That rule does not exist, and mass lesser vigor is definitely persistable. Note that Persist Spell explicitly changes the Duration of a spell, and therefore that maximum is no longer in force.

If he’s saying that he’s making such a houserule, then that’s his prerogative as DM. I don’t think there’s a lot of merit to that particular change; it doesn’t affect that many spells (and there are much more powerful spells than mass lesser vigor that you can still persist under this rule), but that is his call.

You should therefore ask him to clarify which it is, and if he thinks it is an official rule, you might ask him to show you the rule. Generally, though, many DMs don’t like being “called out” like that, so that depends on your relationship with the DM and the relationship your table has with official rules and houserules. If he means it as a houserule, you could try to convince him not to make it, or you could ask him for an opportunity to change some of the choices you made with respect to your character without knowing of the houserule.

Or just persist something even better, like divine power or something.

Stun, Daze and similar stuff don't impede your movement...

...they make your mind funny.

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While you are stunned, there's nothing holding your body to move. You just can't think right to actually do something. If you take a really hard blow to your head, that won't make your body harder to move - it will make your brain go gonzo for a few secs, before you became aware of what's really happening.

Stun is not about movement, is about senses of what's going on.

Freedom of Movement makes "your body work right", not anything else. It allows you to move, but not allows you to think. You can't think if you're dead. Or Stunned.

Paralysis don't block purely mental actions, so it don't block "thinking". Slow makes your body... well, slower, but it doesn't affect your thinking. Web is... well, a web. It hinders your body, not your mind.

Stun, Daze, Dazzle and similar stuff, on the other hand, makes your senses go wacko, so they aren't really blocking your movement. Stun never stopped you from moving, it just stopped you from thinking for a while - and since you don't think, you don't act.

So, the point is,

If something affect your senses, Freedom of Movement can't help you.

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Think like a "Houdini Effect". Houdini can escape from almost anything, considering that he knows what's going on. If you throw him with a concussion inside a closed coffin... well... he will stay there.

So, to determine what Freedom of Movement removes or not, use a simple rule:

Why I can't move?

• If you can't move because a spell or something is hindering your body to move, like Web, Freedom of Movement can help you.

• If you can't move because a spell or something is making your brain go gonzo, like Stun, or because your body becomes something that can't normally move, like stone from Flesh to Stone*, it won't help you.

*Flesh to Stone don't impede your movement, it merely limits you to the movement that a stone statue is allowed to do. A "Freedom of Movement"-ed and "Web"-ed person would become a completely untangled stone statue.

Also, read Freedom, the 9^th level spell:

The subject is freed from spells and effects that restrict its movement, including binding, entangle, grappling, imprisonment, maze, paralysis, petrification, pinning, sleep, slow, stunning, temporal stasis, and web. To free a creature from imprisonment or maze, you must know its name and background, and you must cast this spell at the spot where it was entombed or banished into the maze.

Emphasis mine.

Freedom removes a bunch of effects, like Flesh to Stone and Stun. It would seem rather... strange to say that a way lower-level spell can do almost all the things that a 9th level spell can. Freedom is Freedom, not Freedom of Movement.