The way this dialogue reads to me it seems string tension and string stiffness or flexibility are being interchanged/conflated. The two characteristics certainly correlate about Roto 77 flats but they're two different aspects of the same strings.
that's what I wanted to point out.
if a set of Ernie Ball Hybrid Slinky has the same tension, that doesn't mean that it will have the same flexibility, due to the different construction.
stiffness/flexibility is how a string bends. the tension is the pull expressed in Kgs/Lbs, and this last information can be easily noticed with the truss rod movements.
so, IMHO the Jazz77 just have an average tension, but a stiff feeling due to less flexibility.
another example? the BS66 have less tension than a set of Ernie Ball Hybrid, because once I mounted them, the truss rod had to be loosened.
however the Swing66 have more stiffness/less flexibility, so I had to lower the saddles on the G and D.
last example: everybody says that the La Bella 0760M are extreme in tension, but... they have the same tension as a Regular Slinky set of Ernie Ball (50-105).
few years ago I used to string my basses with Regular slinky, then I decided that one needed flats, and I went directly to the La Bella 52-110, which I like.
well, the truss rod didn't move (even after 7 years), but I had to rearrange the saddles. yes, the La Bella are stiff, less flexible (the outer wrapping is flat, so it's harder to flex/bend), but the actual tension wasn't higher.
a few months ago I decided to try the Jazz77 (45-105) on this particular bass, switched from La Bella, and had to loosen the truss rod and raise the saddles.
so the tension is less than the La Bella Jamerson or the Regular Slinky. they are just stiff strings compared to rounds of a similar gauge, which is normal.
if you want flat with more flexibility, go with D'Addario Chromes, they are softer.