For this to be true, then it must be true that trial-run promotions very frequently fail, so they keep the person in the role they perform best in. I think that's not the case. I think trial-run promotions lead to promotions about equally as often as no-trial-run promotions.

The same people end up at the same end rank, they just take lower pay for a year to get there. And that one year drag compounds because raises are %.

Anyway we're likely disagreeing in an entirely vague way. Of course my leadership skills should be evident if I'm going to ask to be Lead, so yes day1 leads aren't starting from 0. But a company's surest bet for who to hire as Lead is me, so why should I put up with them telling me they just aren't sure yet? All hires into new roles are very uncertain, and I'm the most certain, so I get the role. Someone more certain than me is a person with 2yrs of Lead on their resume, but they get Lead 3 pay, and I'm not asking for Lead 3 pay. You're hiring a Lead 1 and I'm sure surest bet (inside the org or out) and we all know it.

Or go ahead whisper promises of a promotion in the ears of two on my team and watch them butt heads as they try to act out the phantom authority you've given them. A politicking horserace like that has a vastly worse impact on the company than just pulling the trigger and naming one of us Lead 1 even if we're obvious greenboots for a year.