Can you let gaia fight back immediately when it take any damage ? specialy tinker's bow and cross bow , because everyone in my server use ccross bow killed gaia , it just like an idiot stand there and they beaten it like a moron...

You are providing very little information.

Hes saying the tinkers weapons are doing way too much damage to the Gaia Guardian and it's making the boss fight too easy, maybe even causing glitches in fight phases?

I mean, if you're complaining about balance when using another mod, that's your own problem. That's like saying you need to make your mod harder just because you use DE and it's too easy now.

also there should be the damage cap of 25 unless tinkers is being dumb and directly setting health

I think that might be what the issue is. Either tinkers is bypassing the damage cap, or the damage cap isn't working properly in the new version.

The other issue is if you stand rigbt at the edge of the arena, the Gaia Guardian does not start to move around. It stays still not moving, resulting in an easy kill no matter how much damage you do as it never fights back or moves.

..... i mean Gaia take tinker bow any damage , he didn't move

...Gaia was hurt didn't moving

That's an issue I know for a long long time, it doesn't even involve any other mods than Botania to make it happen:
a) get a Terrasteel/Gaia ingot,
b) go to the Gaia arena,
c) activate the ritual,
d) run as fast as you can to the border of the arena,
e) grab your Terra Blade and spam clicks until Gaia is dead,

Gaia won't even move, nor activate mob waves...