The point would be that there is a trade away of value by replacing Gillette. I would hope that it would be net positive, but it is hard to say and it depends on how many jobs are supported and where the money comes from.
There are 1,300 jobs there right now. And according to their website "The South Boston facility adds over $300 million to the Massachusetts economy annually." That money comes from manufacturing here and selling product largely out of state.
https://boston.pglocations.com/about-gillette/
So if 1,300 jobs go away, including manufacturing jobs, and $300 million disappears from the Massachusetts economy every year then that is a lot to make up before you get to net positive with whatever you can dream up replacing them.
More importantly, once you replace the parking lots at Gillette, then there is still underdeveloped land in the area that is better on balance to redevelop than displacing Gillette.
Replacing the surface parking and keeping Gillette is optimal for the foreseeable future.