Why would they [FIA kerb RBR's ability to win] unless RBR did something illegal?
F1 is a commercial sport, like most others.
It needs sponsors.
It needs TV deals.
Bernie is doing a fantastic job, but at some point, even he wont be able to sell a product which is attracting fewer viewers.
Without TV viewers (and the sponsors which come with it), F1 will simmer down.
Sponsors can choose to support another sport - they only care about return on investment - so they will happily jump ship if they get their name to more viewers, by sponsoring another sport or team, for the same amount of money.
During the Ferrari dominance (with MSc), the FIA brought in measures which they felt would prevent Ferrari from dominating.
Also, in 1994 and 1995, when MSc was winning with ease, they introduced refueling to make racing more exciting and unpredictable.
A few years ago DRS was brought in to address the issue of processions.
Its all about making the sport more exciting/unpredictable and if that means preventing a single team from winning repeatedly/easily, then it shall be done.
It is certainly up to rival teams to step up their game. But it is also up to the FIA to help solve the issue.
How sad is it, that weeks before the race weekend starts, we know who the winner of the race is likely to be.