Vanilla Doom had a configuration file where one could redefine key bindings (there was 10 total) to anything player wanted. But, yes, I believe custom configs were uncommon (even mouselook was frowned upon amongst the players I knew[1]) and modern gold standard of WASD+M only became a thing after Descent and Quake 1.

https://doom.fandom.com/wiki/Configuration_file#Keyboard

[1]: For a childish reason - being considered not a "true" way of playing. Although maybe that had some rational roots too, because back in the day mices weren't particularly good - bulky with heavy balls and imprecise with lint-hungry rollers and simple low-resolution sensors.