Just read through this and thought I'd wei (pun intended) in. I think to judge a company on events that occurred several years ago which they admit to and even offered to replace years after warranty expiring is far from garbage.
I have dealt with Mionix Support in the last year or so and they advanced shipped my 2 brand new mice after failures on mine, and i have been using them solidly since then.
These guys aren't a massive company, and it sounds like your experience was due to a support agent who no longer represents the services they provide.
Completely berating a company because a product made EOL years ago, a team member no longer with the company and a good faith offer to sort you our YEARS after the issue occurred is unreasonable.
I'm coming from the perspective of someone who's worked in warranty for PC parts and peripherals, not from some fan boy defending their favourite brand. Mionix can take care of themselves, I just wanted to provide an opinion to anyone else reading this thread.