To state the case against LL for the record: he's a 56 year old Wisconsin goober whose entire D1 resume is going 25-20 in the MAC over six years, at a program that's a historic backwater, but wasn't exactly a dumpster fire when he got there.
Can you just toss out anything that happened in D3 where there aren't any scholarships? Arguably.
Were his first three years at Buffalo less than you would expect from a future Big Ten coach? Arguably.
Are the two years after his 2018 breakthrough kinda less than you might have hoped? Arguably. (Not his fault they only played 5 games this year, but they only played 5 games this year)
Does the whole Buffalo resume in general feel a little Al Golden-y? Arguably.
Is he just kind of a ho-hum guy that's it's hard to see as a galvanizing figure? Arguably.
Could basically every word of the above have been said about Jerry Kill when Minnesota hired him? Arguably.
A couple of comments from your breakdown:
Buffalo had one winning season since 2008 when he took over in 2015. Going further, they've only had two winning seasons since they restarted the program. Going further, SRS (football reference's rating system based on strength of schedule, scoring differential, etc.) is saying they played way over their heads in their heads in that successful 2013 season. This isn't meaning to discredit that season's success but speaking to the lack of talent within that roster.
The 6-6 season in year 3 was only their third .500 or better season since the program restarted in 1999. 6-6 at Buffalo is really saying something, historically.
In the two years after his 2018 breakout (10-4), his teams have gone 13-5. That's a better winning percentage than his breakout year.
Diving back into the analytics, best Buffalo seasons since the program originally started since 1962 (using SRS):
#1 - 2020 Season (by a million miles)
#2 - 2018 Season
#3 - 2019 Season
#4 - 2008 Season (Turner Gill's magical season)
Kill is a factor for why, beyond his really strong background of success at an established program (Whitewater) and a crap program (Buffalo), I have Leipold as my #1. It was a big miss for the program, as Kill got Minny back on the tracks after the Brewster disaster and likely would still be giving us fits if it wasn't for health issues.