I feel that we should be able to upgrade more than one troop at a time in the lab because then it would be much easier to upgrade troops and spells to the max and since you can upgrade one than one building at a time depending on how many builder huts you have I think you should have the ability to upgrade more than one troop or spell too
You are right, it would be easier. Should they make walls cheap so that would be easier? Should they make everything take half the time to upgrade so that'd be easier? Easier doesnt mean better. The game shouldnt be quick to finish. It's better that it takes awhile, and there would be no reason for you to gem your current upgrade if you could just start another, which means Supercell would lose money, and they aren't in the business of losing money.