[anthk]

Spanish has rules for verbs ending with -ar,-er- and -ir save for few exceptions. Still, RAE should have accepted "conducí" as "conduje" long ago (and the rest of declinations/verbs such as traducir, reducir...) IDK about Greek.

If we are using two valid ending forms of Subjunctive (-era/-ese) since forever, IDK why couldn't we set these irregular verbs back to regularity.

[schoen]

Greek has verbs with different "thematic vowels", which are sort of like the Spanish conjugations, but not exactly the same thing (although I think both varieties of verb groupings probably have a distantly shared origin in Indo-European).

The Spanish conjugations -ar, -er, and -ir derive from Latin conjugations, which are usually analyzed as having four different regular conjugation patterns (there are long and short e, giving -ēre and -ere, in addition to -āre and -īre), although one can choose to make additional distinctions.

Generally older Indo-European languages have more complex morphology than newer ones, including more paradigms and more irregular forms. Ancient Greek verbs are definitely morphologically more complex than modern Spanish verbs.