Atlas at his maximum size possess Excess of Class 100 Strenght, that means he can lift more and more of 100tons.But it's not all.He can also fly and transform into a energy form like Wonderman as we saw when he was controlled by Nefaria, and in that state is invulnerability is at Wonder Man level i think
He can't actively turn into an ionic energy state, he only did that when Nefaria mucked around with him.
Pym uses the pym particles to grow, at his tallest he's class 60 or so, he also has a few gadgets and stuff, and as Yellowjacket has a bioelectric blast.
Atlas was subjected to an ionic treatment similar to Wonder Man's, thus gaining super strenght. Then he got pym particles, as he grows, his super strength grows proportionatly, endowing him with class 100. This also gives him enhanced stamina and resistance, whereas convential arms hurt Pym, Atlas becomes more durable, and at his tallest almost nothing can hurt him.
Atlas takes it.