TCU had a 0% chance of winning the national title under the BCS when we were in the WAC, Conference USA, or MWC. We don't even need to debate that, we saw it objectively in 2009 and 2010. Utah saw it in 2004 and 2008. Boise saw it in 2006, 2008, & 2009. ZERO. None. With the CFP it took an exceptionally rare set of circumstances and a multi-year process, to get a single G5 team in to the playoff, so it was only slightly better. Any system that at least gives an undefeated team a chance is objectively superior to one that 99 times out of 100 excludes them entirely.
First of all, we just saw Texas and Alabama played a game whose result was ultimately meaningless, because both the winner and the loser of the game got in over an undefeated team. So we know the results of the regular season is not as sacrosanct as you suggest.
Second, the current system is one where an undefeated team, both inside and outside the power conferences, can be excluded from the national title race. It happened in the BCS (Auburn), it happened in the 4 team playoff (Florida State). While it's theoretically possible that will happen to a G5 team in the 12 team playoff (1 undefeated G5 champion is guaranteed to be in, a second one could theoretically be excluded), it is literally IMPOSSIBLE to happen to a Power 5 team now. That's a step in the right direction.
So yes, a 12 team playoff means every single Power Conference team and 99% of G5 teams have a chance to "settle it on the field", whereas right now they do not.