One must be extremely hesitant to deligitimize minhagim that have lasted generations if not hundreds of years or more. When I was a child, the shatz never said ga’al yisrael out loud, and I surmise that most of you out there who are over 50 and certainly over 60 can verify this. In the last 25-30 years or so, the minhag of saying it out loud has gained momentum and as others have pointed out , it is probably the correct way to do it. But to knock the “old” way? Absolutely not.
On a related note, if you do a little research, you will find that ending any phrase with a kamatz instead of segol in the davening is a recent invention beginning with the haskalic medakdikim in the 1700s, some of whom were at best only quasi-observant Jews. You will not find any of these changes in nuscha’ei edot hamizrach, and there is a reason for that. This includes gefen-gafen, eved-aved, gever-gaver, geshem-gashem, and many other changes which NEVER EXISTED in previous nuschaos. And yet, almost all of us say gafen, aved, gaver (geshem has made a serious comeback). A mistake? Yes. But it is entrenched and accepted (find me an ashkenazic siddur that prints shelo asani eved), and to deligitimize it may be intellectually stimulating, but mezalzel bichvod our fathers and grandfathers, and it would be fruitless as well. That’s the way it developed and that’s the way it is now. We have bigger problems to solve than these.