Even damaged leaves can still contribute to the tree. Leaves that are cut off cannot contribute. If the tree needs more leaf surface it will grow some more to compensate. Cutting damaged leaves is to make us feel better. It does nothing for the tree.
I have been caught a number of times by rain. A lot of the rain falls off the leaves. When a tree is in the ground that rainfall is directed to the area where there are plenty of roots - the dripline. With our trees in small pots the rain is directed outside the pot and mostly misses the roots completely. The better developed the canopy the more rain it will shed. Yours is not so dense as to shed all the rainfall so some should have reached the roots but perhaps not enough. Never assume that rain has watered your trees in pots. Check, or even water anyway, just in case.
Just keep an eye on it for the rest of the season to make sure it doesn't get worse which could indicate disease rather than moisture stress.