What do you mean by "I'll make sure they'll answer them"? Are you a reporter? But if this is a bug report thread now, here I go:

I have and one of my friends had the Logitech G502 LIGHTSPEED mouse. It has a problem with it's mouse wheel.

I've done the debugging a while back, but maybe I can get the logs again. Basically when using it wired it only uses the regular mouse wheel events, but when using it wireless (most of the time) it uses both highres mwheel events and regular ones. Confusing all apps. To add to this, the regular events seems to be simulated by software, based alongside every 5th (? maybe it was a long time ago) highres event. While at seemingly random times a full "click" of the mouse wheel just doesn't register the required number of highres events, making the "normal" one also absent. I tough this was a hardware issue, as when it happens you can go back and forth and it won't register it at all, however it doesn't happen when pugged in.

This is probably some kernel issue if I'm being honest, all I know is that on Windows it works perfectly. But I am using KDE and I have not debugged this mouse on any other window manager.

I truly don't know if this was the type of reply you were looking for, if not: Sorry for wasting your time. (There's also a KDE bug when editing widgets or when turning the screen off and on, but that's not input device so)

Most important feature whoch Gnome has for Years.

2 or more Mices at the same time with its own focus. Something that KDE can't handle at all, because those two mice positions are figthing for the cursor

how can we have relatively simpler touch gestures? mostly what I'm thinking about is long press for imitating a right click, but text selection with popup copy/paste/etc buttons would also be useful.

I would say it's also inconvenient that we don't have a good touch keyboard for wayland, but you probably know that.
maliit is hard to build, afaik not packaged for any distro, buggy and not customizable (or if it is, it is not documented anywhere else than the code), apparently there is no way to limit it's width, which makes usage harder on tablet sized screens. it has also been abandoned by the devs.
squeekboard is not compatible with KDE wayland because of missing protocols.
onboard is X only.

Honestly I wish those developers would focus on the basics rather than esoteric input devices.

KDE isn't stable enough with a regular mouse and keyboard, let alone fancy input devices. It crashes WAY too often and has too many bugs which require the user to constantly have to use the terminal to work around.

KDE: get your priorities straight and focus on basic stability and usability first.