An argument could be made that the MWC hasn't necessarily "fallen"; it's just become the new Conference of Cannibals (usurping the PAC-12s role) due to parity.
As for Air Force, I don't know why anyone is surprised. Anyone who was actually paying attention knew they had one of the softest SoS's in the entire country, and everyone who knows anything about CFB knows that while the triple option does well against inferior competition and can occasionally trip up equal or slightly better opponents, it's [generally] not sustainable long-term against quality competition. How many triple option conference champions have we seen in the last 20 years in FBS? Literally none.
AFA does this every year...they have a soft as baby sh*t OoC schedule that they go nuclear on, then they trip up one or two conference mates, and then they sh*t the bed. Which is why they consistently look strong early and have great overall records, but only have one MWCCG appearance (in which they lost).