Well, now F1 has made accounting a sport, so of course RB would try to push the limits.
Will be interesting to see how this will play out.
Since overspend is an easy metric, I am surprised, that there was no agreement on exact penalties ahead of time, especially since the results will always come in one year after the championship was decided - so there will always be a reluctance to penalize for the already decided season.
Applying penalties to the running season would work better (but then, remember e.g. the Force India to Racing Point transition, where constructors points were lost - so would be any penalties).
It should probably be really simple: Up to a lower limit apply a financial penalty. Probably in the 1 Mio. overspend range. If someone crashes into you in one of the last races of the season, you should still be able to afford a new chassis for the rest of the season, without getting a sporting penalty. Just make it a straight up deduction from next year's budget, plus interest/inflation and flat fee/fine for the FIA having to handle the issue.
Above that practical limit, deduct twice the percentage of overspend from the points for the currently active season, from all drivers and team, for the entire season. Overspent 3% last year? Lose 6% of this year's current and future points (plus a higher fixed fee/fine for processing).
And above, say, 10%: straight up disqualification from the running season, and no payout of constructors championship prize money for last season. Basically end the team.
See, that's not so hard. There's no reason to overspend, penalties are clear, and there's plenty of headroom to have misunderstandings of the rulings and creative accounting with known risks involved. And if you take a higher risk: well you know in advance, that you're playing with fire.
On a positive note though: Only one team slightly overspent - and at least tried to do so in a "sporting" way - by playing the rules, not just flaunting them. This might make F1 just that little bit more sustainable, and if the method hold true, maybe can be applied to other top series as well, e..g WEC or WRC, maybe even DTM and FE. If you can then even allow more technical liberties, while putting in place stricter financial restrictions, this could lead to more innovation on a regular basis.
Of course, it will likely take another couple of years to see how well the budget monitoring really works, and how much money can be siphoned past the FIA's external controllers.