List all the starting QB's. Separate them into two groups: The ones you'd prefer over Mitch/Foles, and the ones you wouldn't. If those groups are the same size Mitch and Foles are league average. If not, they're not. Spoiler alert: The first group is larger, thus the statement you made is incorrect.
Ooh, so this is actually kind of fun.
O.K., this isn't a ranking, but rather a grouping, so no squabbles over a place here or there.
I've highlighted the middle (average) group of quarterbacks. Guys, please tell me which ones you would take Trubisky and Foles over.
(HINT: Trubisky and Foles are among the worst starters in the league, very much NOT average. In fact, I'd give my big toe for any of these average quarterbacks.)
Top-ish 11
(please allow for margin of error)
Patrick Mahomes
Josh Allen
Tom Brady
Aaron Rodgers
Deshaun Watson
Lamar Jackson
Kyler Murray
Russell Wilson
Drew Brees
Joe Burrow
Justin Herbert
Middle-ish 11
(the definition of "average")
Ben Roethlisberger
Baker Mayfield
Derek Carr
Dak Prescott
Matthew Stafford
Phillip Rivers
Kirk Cousins
Jared Goff
Alex Smith
Carson Wentz
Jalen Hurts
Bottom-ish 11
(among the worst quarterbacks in the league, although some certainly have brighter futures than others, potentially)
Jimmy Garoppolo
Daniel Jones
Teddy Bridgewater
Matt Ryan
Drew Lock
Ryan Tannehill
Gardner Minshew/Mike Glennon
Sam Darnold
Cam Newton
Tua Tagovailoa
Mitch Trubisky/Nick Foles
Quibbles can certainly be made with my grouping as it relates to individual players,
(for example, someone might say Tua is better than Wentz or so-and-so is better than Goff, etc.)
but
generically speaking, the bolded above are your average quarterbacks in the league.
This is not an exercise in ranking quarterbacks, but rather an exercise in asking yourself this question:
Can Trubisky or Foles sniff any of those guys' jocks?
If you take any of those bolded guys----those average guys----and put them in a Bears uniform, they're either immediately the greatest Bears quarterback of all time or very likely to be in their future.