Mathematically it is the exact same! If you take 400 races to get to S instead of 72, just means you finished in the back half affecting less players in each race while also giving some points to those that finish ahead of you. Of course if you do it the fast way you 'steal' less poles and fastest laps.
Tanking DR is giving points away, unless there's a reset and the points are permanently removed from the system. Actually when the DR up reset glitch still worked the people that abused that were the real Robin Hoods of the game

Nowadays any DR reset only causes deflation, making A+ rank a little more exclusive with each reset. No need to remove the 75K cap, simply reset more people and it will keep getting harder to reach!
Anyway this whole DR system is pretty inconsequential anyway as match making looks at SR first. Max SR.S is not a big group, DR only matters when your SR is low (SR.B is 55%, SR.C is 25% of the player base) and there it gets reset... So full of contradictions
Why matchmaking works so weird:
of the 6.5% SR.S players.
D S 24,129 36%
C S 14,653 22%
B S 22,602 33%
A S 4,802 7.1%
S S 1,202 1.7%
Any time you're falling below 95 SR, high chance you end up with D/S and B/S players.
Those numbers are still further split down over 3 regions, 3 dailies and 2 FIA races. A room full of A/S is rare.