It's a tough question to answer, a lot depends of where your organization is at development wise at this point. Generally if you have a good pipeline and have solid healthy players at most positions, then a 6 WAR player could make a big difference. If your pipeline is poor, and you have many holes, then generally 3 2.0 WAR players would be better. How healthy your players can stay plays a big role as well.
The Angels are in the latter position. Their big 3 (Ohtani, Trout, and Rendon) can't pull the load for the remainder of the team, essentially they are pulling them down. There are several problems, too many veterans who are not even 2.0 WAR players, poor minor league development (the pipeline), poor organizational plan and evaluation techniques, injuries hurt to some degree as well. We are kind of the inverse of the Dodgers, not that they are perfect. I would say the Dodgers are not efficient, they are wildly outspending the Angels to help create such a wide comparison gap. Same with the Yankees. Both the Yankees and Dodgers have much better baseball operations departments than the Angels, and better young player development. Arte is trying to emulate them, but he is not spreading the investment wide enough or high enough.