Simplicity isn’t the goal of languages, but communication. England historically had a lot of different languages and dialects that tried communicating with each other, so the language got simpler to speak and understand.

German, Russian, Italian, etc. all existed in relatively homogenous so information density was far more important. Some languages use gendered articles, which also increases understandibility (if someone is mumbling a word you can still guess it).

Sie is actually a really interesting case, because it shifted meaning over time, from being a sign of respect, to being an indicator of closeness, but it still carries information.

"Lassen Sie mich in ruhe“

and

"Lass mich in Ruhe“

both translate to "leave me alone", but the first one carries the information that these people don’t know each other and it might make sense to interfere.

And most importantly: your comparison to irregular verbs and idea to just change the word doesn’t make any sense. Gender is part of the word, so creating a new word would just be a waste of time, so it’s the same thing as just learning a new verb. Irregular verbs are a completely different thing since they don’t follow the rules of the language, so you have to learn two extra words, instead of just learning one and following the rules.