I think, for me, I avoid jQuery because I haven’t found a use for it (for apps that I work on). I try to be mindful of code dependency and maintenance cost that I would create by installing a package. I want the code that I write today to be able to stand on their own for a long time. 
As for bundle size, what I’d do in your shoes is to compare the production build size before and after installing @ember/jquery. If the difference is acceptable to you and your team (again, in the context of your app), I think it may be okay to use the package.