I agree with you on that one. It just makes stuff a bit more complicated than it has to be. Especially, if there would have been options to include both control methods.
Anyway, Colseg did some work and created alternate keybindings, which you can find here: http://forums.eagle.ru/showthread.php?t=130459
Just to make it a bit easier, I also uploaded my jostick default.lua which incoperates those changes by Colseg.
Just download the file in the attachment and paste it into DCS World\Mods\aircraft\MiG-21BIS\Input\Mig-21\joystick.
This will not change your keybinds, it will just give an option to use "alternate" keybidns for many HOTAS related switches. default.lua