I am wondering if AM's search function can not replicate Gmail's search bar in Gmail webmail? I can totally understand if it is not the same since AM simply can not find what it has not downloaded.
I tried testing that omnibar and it did work all the way back to searching 2014's email with the RAR attachment I was looking for - simply by using dota.rar string. But then again Gmail's webmail has the data and can load it on the fly, so it makes sense