The issue with DSR was that depending on the order you won your games in (and subsequently, which stages you won on), you would be able to cp different stages a different number of times. This was first brought to my attention at Zenith when PP had to play on FD vs. M2K twice in GF2 because M2K "broke serve" by winning on PS. This basically meant that it was more important to win on your own cps than it should be. Winning on the opponent's cp and losing on yours should leave the rest of the set playing the same as winning on your cp and losing on theirs.
So the root of the problem is DSR is based off of what stages you win on. BSR addresses the issue by basing stage selection off of the independent choice of the player regardless of whether they win the cp or not. If M2K wins on PP's cp, it doesn't mean he instantly gets to repick because PP can still ban it (unless he banned it last time). The number of times you can play a stage is limited because players are in control of when they play the harder cps. Here's a test set of Falco vs. Marth to show how it would play out based on each ruleset (cps based on my personal beliefs of which stages are best):
DSR
- They strike to BF and Falco wins [1-0]
- Marth cps FD and wins [1-1]
- Falco cps DL and wins [2-1]
- Marth cps PS and wins [2-2]
- Falco cps FoD, and they play it out (slight favor for Falco because he won game 1)
No problem when they alternate wins, but when they don't however...
- They strike to BF and Falco wins [1-0]
- Marth cps FD and wins [1-1]
- Falco cps DL and LOSES [2-1] <-------- Because of this match...
- Falco cps DL and wins [2-2]
- Marth cps FD AGAIN and wins [2-3] <--- ...Marth gets to cp FD twice
This means not only did Falco fall behind in the cps for losing, but he guaranteed his opponent can repick his best cp. This IS a fair ruleset because Falco got to cp his best cp twice, so Marth did as well. The problem with this is that DSR does nothing to influence the set. The set is played identically when you have no bans at all. Players going back on forth on the hardest cps not only makes the first match disproportionately more important, but it has less stage diversity because each player is just scrambling for their best cp.
With BSR:
- They strike to BF and Falco wins [1-0]
----- Falco bans FD
- Marth cps PS and wins [1-1]
----- Marth bans DL
- Falco cps FoD and wins [2-1]
----- Falco bans PS <------------ Can't reban FD
- Marth cps FD and wins [2-2]
----- Marth bans FoD <---------- Can't reban DL
- Falco cps DL
Set 1's Stage Order w/ DSR: BF, FD, DL, PS, FoD
Set 1's Stage Order w/ BSR: BF, PS, FoD, FD, DL
Same stages, but the order is swapped (the +2 cps get swapped with the +1s).
Second set with BSR:
- They strike to BF and Falco wins [1-0]
----- Falco bans FD
- Marth cps PS and wins [1-1]
----- Marth bans DL
- Falco cps FoD and LOSES [1-2]
----- MARTH bans FoD <------------ Can't reban DL
- Falco cps DL and wins [2-2]
----- Falco bans PS <---------- Can't reban FD
- Marth cps FD
Set 2's Stage Order w/ DSR: BF, FD, DL, DL, FD
Set 2's Stage Order w/ BSR: BF, PS, FoD, DL, FD
MORE stage diversity, but the cps are still balanced, and the order of victories and the stages they take place on are no longer relevant. Hopefully this is all laid out clearly enough. This stuff can get really confusing even if you already understand it, so if anyone needs clarification, lmk. Disclaimer: I realize these are just hypotheticals and that stage choices don't usually play out this way, but even when players have differing opinions about what stages are the best for them, their inherent value to the player making the choice are the same so a player will never be able to complain about the stages that got played.
