since 80's i preferred wasd keys
using one hand for up/down and another for left/right always was very confusing for me, i always got surprised why that was the default, or the only option available that time - but perhaps that was only me, as i actually played lots of japanese msx games before starting playing zx-spectrum ones (i lived in brazil that time, msx was more popular than zx-spectrum back then there)
Eye of the Beholder obviously, but it's certainly unusual that you preferred WASD as a key combination in the 80's, considering that virtually no game or system in that decade ever used it! It came with the advent of first-person 3D shoot-em-ups on the PC in the following decade.
WASD can be suitable for games that use many keys, which is why and what for it came when it did. For simple games typically using just 4-5 keys as is the case with most ZX Spectrum games, OPQAM/Space is the generally preferred combination - it's no coincidence that over 90% games from that period used it.
In the present case, because it's just 3 keys, QWM/Space works fine too, really. Hell, anything with two keys for movement in one hand and one key for firing in the other hand would work equally fine for 3 keys.
it was indeed unusual, i used that on all games allowed to redefine keys (like those spanish ones from Dinamic, Topo, Opera, etc.), as they were much more comfortable for me (like using cursor keys on msx in the same years) - it was a surprise for me seeing these same keys being used by default on dos games eecade later