Windows also supports flight sticks and Steering Wheels. Drawing Tables and Microphone Input.
My Mouse is pretty old, its a Razer Abyssus V2 from 2014, but thats way newer then 2007. Just searching on Amazon gives me 2 out of 10 Results in the Top 10 that actually have any additional Buttons besides LMB/RMB and Mousewheel Scroll. You can not expect every Player to have extra Mouse Buttons or specific Input Devices. You can recommend People should have a specific Input Way, like Controllers or extra Mouse Buttons, but your default PC Input should be playable completely by LMB/RMB Basic Keyboard.
*Edit: It is fine to offer additional not needed Functionality on extra Buttons, or bind Inputs to those in addition, Zooming by scrolling Mousewheel, or swapping Weapons by extra Mouse buttons i.e., but every key Input, like Movement/Swapping Weapons/Attack/Block/Interact/Whatever should be playable with Core Input of your Device only. Thats Keyboard and the 2 Mouse buttons for PC, Controller for Console and single finger Gestures for Smartphones.