Avogadro's gas Law doesn't make sense? (it does actually)
Oh it definitely makes sense since it allows us to describe a lot of systems with very simple formulas.

The problem is that this law assumes "ideal gases" (just like the ideal gas law) where atoms/molecules are "points" (no volume) and they don't interact with each other. This works well at rather low temperatures, low pressure and for gases without strong intermolecular interactions.

But you are correct, there are problems and the law doesn't work in a lot of cases. For example if you go to high pressures the volume of the indiviual atoms/molecules does play a role, since if they are bigger the available space will be smaller and the pressure will be higher than predicted by the ideal gas law.