Yeah, this bothers me a lot with mine too (an RM2). I can't believe how heavily I have to press to get full line width on many tools, it's harder than I press when I use an eraser on a stubborn mark in real life.
Responsiveness wise... the latency on common actions has increased incredibly in the past couple of years. Not pen drawing, that's still excellent, but general UI navigation and recognizing taps and long presses and whatnot have really gotten bad. At this point I've got it rolled back to 2.x almost all the time, which is also a whole lot more moddable than 3.x. I like many of the UI changes and additions in 3 (except infinitely vertically scrollable stuff, that keeps screwing up and interpreting taps and swipes as vertical scrolls when there's absolutely no additional content to show, so it just stops responding for a second while it scrolls three pixels down, and I would be thrilled if I could disable it completely), but not at the cost of responsiveness.
Dual boot (disable updates and install any two you like): https://remarkable.guide/tech/dualboot.html
Some lower level details here: https://github.com/ddvk/remarkable-hacks/issues/304
And installing a specific release is largely automated: https://github.com/ddvk/remarkable-update
Last time I did it, I just did it manually - back up the OS version you want over ssh, then restore it whenever you want (on the non-active partition). And screwed it up the first time, and had to do a recovery: https://github.com/ddvk/remarkable2-recovery (requires using the contact pads on the spine for USB access - not too hard to solder up a pogo pin thing, but might take some time to get the parts).
So I'd recommend the automated way, though I haven't tried it yet :)
There's a (single) relatively active discord server if you want specific Q&As with other people too, or to double check whatever the current recommendations are (probably do that, as I'm somewhat out of date): https://discord.com/invite/nQ6nHwfDfc
And do definitely back up your data partition before making any major version movements tho, in case something doesn't work right and you need to roll back. I forget if/when that's necessary, but it's a good safety net just in case. And <8GB isn't much to store just in case.