Usually you would say "improving the efficiency of x and y". In this case at the end of the sentence it should be "improving the models' efficiency" or just "improving efficiency". I don't think it's "wrong" and it's obviously clear what they mean, but I agree that the phrasing is a little awkward.
"the" is redundant is probably what GP means.
You would just say "improving efficiency". Whereas theirs is like: "Improving the efficiency [... of what?]"
You left out words at the front that are important.
“deliver better quality while also improving the efficiency.”
Reads fine to me. An editor would likely drop “the”.