We can argue over who got in and who deserved to make the field until the cows come home, it happens with every bracket in every sport. There are going to be snubs and things that can't be explained, like why UC Davis gets a first round bye.
Out of those 8 teams you list this team in over that one, the only one I can see that there could be an argument for is Monmouth, but I agreed that the committee left them out because they lost to then 1-10 Albany at home worse than the 7 point margin would indicate.
Despite the fact that I hate having a bunch of teams from one conference going in (why play the regular season) I can't agree that Western Carolina at 7-5 should go in over UND. Compare UND's losses (K-State 38-35, UM 24-23, USD 26-21, NDSU 15-10, SDSU 34-31) to WCU (Gardner-Webb 52-45, Wake Forest 42-10, Elon 37-31, Mercer 49-47, ETSU 52-35). UND lost 5 games by a total margin of 17 points and all four of the FBS teams are in the playoffs. WCU lost two games by 17 or more points and only one team is in the playoffs.
Presbyterian should not make the playoffs just for their nickname. They weren't in the first four out, and while they had a quality win over Mercer, they also played two lower-level teams, including and NAIA opponent. That means they were 8-2 against the FBS, while Harvard was 9-1.
No way I would ever consider UTRGV a playoff team. They played 3 lower-level games, two from the NAIA. Additionally, they lost the head-to-head matchup against Lamar.
I respect your opinion, but I disagree any of the four you suggest deserved a bid. As I said, Monmouth was the one I would consider, but that was an unforgiveable loss and I agree with the 24 team field as it is. I would be more in favor of reducing the field back to 16 and get rid of all the first-round blowouts you note before looking for replacements.