There is a perverse kind of joy in making it work the hard way.
(The other is "I'm old enough to have been using text email since before graphical email clients were a thing and don't want to change.")
and even if it were the truth: navigating mail generally consumes the least time... actually reading the mail and deciding what to do about it takes way longer. another activity where a scroll wheel is invaluable.
Depends on the kind of email you receive.
I'm a heavy VIM user. Gmail supports VIM keybindings and there exist VIM keybinding extensions for all popular web browsers, i.e. Vimperator on Firefox.:wq