If you think about it, Roku's and similar devices have been doing the same basic tasks for years. The only difference is maybe a new audio / video format needs to be added from time to time.
I am pretty sure the issues are not nearly as much hardware as they are the software. A little secret - software coders are getting lazy and sloppy. Especially from the likes of big "don't care" corporations like Alphabet/Google/YouTube.
When Roku releases a newer device with a little more horsepower and memory, most of these coders will get more lazy, spending less time optimizing their code to run efficiently and instead let it bloat because there is now headroom to do so in hardware and they don't want to deal with it.
Those of us with older boxes reap what they sow when that sloppy bloated inefficient code tries to run on lower end hardware. Code which, if properly optimized, would be far more reliable on all hardware.