Our guild one shot the first event on ToC25 this past week with few deaths and we almost had Jaraxxus. We’re up to working on Thorim in Ulduar25 and we have one ten man team attempting to down Yogg-Saron for the first time. The second team is likely only a few weeks behind as they just hit Mimi. We’re doing well, we’re progressing as much as a casual, family raiding guild can expect to and yet some people are unhappy.
So in summation, I believe that gearing alts is great to a degree, but it should never get in the way or hinder 25 man progression.