We have a lot of tabs in our site.yml with a lot of data. The panel became very sluggish, taking 2+ seconds to load. I noticed that if I remove tabs one by one, the performance gets increasingly better.
It doesn’t make any sense to load the data for all tabs if only one can be visible at any single time. Kirby should load just the data for the initial tab, then load data for a new tab when that tab becomes active.