Yes, more redindancy is good and indeed worth having. Still 5 12tb drives are probably yet more energy and heat efficient than 10 4tb ones.

Even if I had 10 4tb for free I wouldn’t use them. Maybe a couple for backup reasons or cold storage, but not active 24/7 for a domestic raid environment.

I actually have 4 6tb hdds that I dismissed for the 4 8tb sdds, and I use two for local backup and keep two spares to replace them when they will fail.

4 8tb in raid5 provide 24tb total space that its far more than I need, and the risk of a double failure is mitogated by a proper 3,2,1 backup strategy in place.