There are both sides.
What if formation lead goes u/s on start? Or gets shot down?
Depending on what you are doing, it is vital that a/c no,1/2/3 does the job that it is supposed to do.
I know that BFJTS formation teaches sometimes resemble square dancing, but it is for a reason: the stude must see and practice the required positions.
Get to the front-line, and I agree, Afghan 1 takes off as him (or herself) as Afghan 1, and the landing order is explained to ATC.
So. The renumbering is OK for teaching purposes in order to achieve the aim, but leave it behind when you get operational.
Can I be an MP now? Pension's better and I won't claim to have my moat polished.
Ladies, my moat is never-ending, moist and slippery. Oink. Fnaar.