Languages with phonetic writing in the modern day likely achieved that through a language standardization process that included spelling reforms.
English's changes in spelling and grammar are mostly legitimized through influential works of the language, hence why you all gotta learn Shakespeare in highschool, you're being taught the history of how the language we speak today evolved.
There is no centralized academy of English grammar, and official dictionaries in English for the most part add words descriptively to reflect how the lexicon is changing in real time.
Put together this all means that the English language isn't remotely broken, it's just old, older than most modernly written languages by a couple of centuries actually.
Funniest part is if you study immigrant settlements in the Americas from all those countries that underwent standardizations, they're all about as "broken" as English looks too, because they're forms of those languages preserved from before standardization came to their homelands.
Japanese and Italian are especially funny since the standardization came into enforcement recently enough that native speakers from Japan and Italy will be bewildered by speakers from the Americas because the speakers from the Americas speak in a way that sounds like their grandparents or great grandparents if they recognize the dialect at all to begin with.
We only refer to MSA when talking about Arabic. Most Arab speakers consider dialects side languages to Classical Arabic. They have never had a transcription throughoutout history. People started writing in their dialects only recently with the arrival of SMS and the internet.
I get that as a new comer to Arabic you probably have come across learning materials for dialects like Egyptian and levantine. But in reality you won't find uni courses for those dialects because academics don't consider them to be proper languages with clear grammar and an established vocabulary.
Actually I chose to learn dialect first because literally everyone who knows anything about the language cautions that native speakers will swear up and down that you should learn MSA and then be completely incomprehensible to you because of how little anyone actually uses it in the Arab world.
I've been working with my teacher for a year and a half now and she agrees that MSA is basically pointless unless you intend to start consuming arabic language news or listening to arabic language political speeches.
BTW this is from a professional cultural expert who's literal job is to prep government workers and businessfolks to be able to engage successfully with the Arabic world, something she's been doing for 20 years now, so I'm pretty sure she knows what she's talking about.
You do you. And you have to take into consideration what your goal is by learning Arabic.
Dialects are definitely easier to learn and more rewarding as it allows you to converse with people and test your advancements. But you won't be able to easily transition to another dialect. Because MSA is the glue that make the intelligible.
Learning MSA will take you triple the time. And I imagine your teacher is both proud of his dialect. But also doesn't want you to drop learning if you were to have chosen MSA
With Japanese, it's more-so that the standardised version is widely used in politics, to strangers, to acquainted superiors, and just in general by default
It's only between friends, within most families (and to acquaintances who regard you as their superior) that you speak... Whatever, really.