Well, you are right. In the 12 and 24 hours races, it's not that important, as you can shift and move schedules easily.
But take a 6 hours event. If you have only 3 drivers - and that can happen easily - you are actually totally bound to one strategie. Example XRR: max 3 stints per driver. A 4th stint would shoot far over the 40%. For FXR it's even more obvious: 2 hours (about 4 stints) are doable, but not a 5th. That leaves almost no room, to change tactics during race. So everytime, something unforseen happens in RL, you cant really react to that. Sure, you can now argue about having enough guys for the weekend. But for example next race is scheduled together with 2 other events in the LFS world. I see your point in those "dont let one driver drive it all" but as you can read, that's not my intention here
Anyway, if the rules stand, we'll have to accept it, but I guess one or more of the smaller MoE teams will run into trouble at one point here.