To me it seems the rule would help teams who have a few guys with big salaries over a team where almost everyone is on a rookie deal.
Specifically, the Rams will have these qualifying deals in 2021: Donald ($19.9M salary), Stafford ($20M), and Hekker ($3.75M). So the Rams would get a cap exemption of $21.825M. And that number would not be any higher if they had kept their first round picks in 2018, 2019, 2020, 2021, 2023, and 2023 since the three guys they would have drafted would still be on their rookie deals and the other three picks have not even taken place yet.
(Note: I assume that all payments made to a player in a given league year count - workout bonus, roster bonus, and salary. (And if it is just salary look for teams to convert workout bonus and roster bonus to salary!!))
AlbaNY_Ram