I've been curious about whether or not the quality of the June Tailor rulers has changed. I think I have acquired all of the JT rulers over time. My newest one is several years old, and the older ones must be at least ten years old (probably more!). I have had no problems with them -- no breakage, no nothing.
Anyway, today I was at Walmart and saw one of the JT's in the sewing aisle. I whipped out my mini measuring tape and measured the width of the plastic at 2mm or just under 1/8" thick. When I got home, I measured the three JT mats I have out at the moment. They all measured that width or less. I suppose it's possible they've changed the composition of the plastic. However, the Walmart ruler felt the same as the ones I have at home.
I honestly don't think the JT rulers have gotten flimsy over time. I think it may come down to how individual people use the rulers. I am what I would call a "slow" quilter, never rushing, and I think that may be why all the rulers and mats I have seem to last. Many years ago I worked faster and remember nicking some ruler edges with my rotary cutter. That never happens to me now.
The harder plastic of the Stripology rulers is probably stronger than the softer plastic of the JT rulers, but I wouldn't call the JT rulers flimsy. They probably do require a little more care when using, though.