nope I agree with you. I think you're correct. You made observations based on your experience. They were'nt subjective or presumptious, so they can't be wrong. They're facts. If the frame flexed, the frame flexed.
Uber Clydes have not use for lightweight 531 tubing. I usually recomend rigid mountainbikes or the more entry level, heavyer (thus more beefier) road bikes.
I think an old Varsity frame with a round fork can hold anyone that is capable of riding it.
Of course upgrade the components to your liking. I not saying to use the low end stuff, but I also would not recommend for example "Dura Ace cranks" to an uber clyde. Something more durable is in order.