As others have said there is too much going on to know the exact cause, other than the Trek dealer's response; which may or may not have analyzed the situation.
If I understand the latest situation, you basically accelerated two crank revolutions, (Estimate 7' circumference at 2:1 ratio = 28') and shifted under force and dropped the chain that (I'm guessing) tore up the chainstay. Generally modern drivetrains with ramps and pins to assist chainring shifting have eliminated a lot of issues, but trying to make a 16t jump (compact crank?), especially after multiple hard shifts may be more of a culprit.
Regardless of the actual cause, to be specific to your stiffer question, I'm not sure there is a lot of published data of bike frame lateral stiffness. Apart from that you may only get educated and uneducated guesses. I did find an article that provided some data, although it is 6 years old, it does give tested numbers for some frames. My recommendation is to pursue data driven recommendations and hopefully find testing of current frames. Possibly contacting "Tour" magazine for more current data.
https://www.cyclist.co.uk/in-depth/1...rame-stiffness
John