They already made literally the ideal button configuration for a pen and it's this

• A big central button that's easy to find by feel, and long so it covers a lot of grip positions
• Two little function buttons that are separated a lot physically by being on either end
• Really nice and clicky

Literally my take is they should have put exactly this button on the apple pencil - and kept the double tap/squeeze gesture even, just add real buttons so you could do more. I don't want haptic feedback or a radial menu... I just want to press a button