Still trying to get good.

The requirements are forever shifting, and so do the applied paradigms.

I think the first layer is learning about each paradigm.

You learn 5-10 languages/technologies, get a feeling for procedural/functional/OOP programming. You mess around with some electronics engineering, write a bit of assembly. You write an ugly GTK program, an Android todo app, check how OpenGL works. You learn about relational models, about graph databases, time series storage and key value caches. You learn about networking and protocols. You void the warranty of all the devices in your house at some point. You develop preferences for languages and systems. For certain periods of time, you even become an insufferable fanboy who claims that all databases should be replaced by MongoDB, or all applications should be written in C# -- no exceptions in your mind are possible, because you found the Perfect Thing. Temporarily.

Eventually, you get to the second layer: Instead of being a champion for a single cause, you start to see patterns of applicability.

You might have grown to prefer serverless microservice architectures driven by pub/sub event busses, but realize that some MVC framework is probably more suitable for a 5-employee company. You realize that development is not just about picking the best language and best architecture -- It's about pros and cons for every situation. You start to value consistency over hard rules. You realize that even respected books about computer science can sometimes contain lies -- or represent solutions which are only applicable to "spherical cows in a vacuum".

Then you get to the third layer: Which is about orchestrating migrations between paradigms without creating a bigger mess.

Your company started with a tiny MVC webshop written in PHP. There are now 300 employees and a few million lines of code, the framework more often gets in the way than it helps, the database is terribly strained. Big rewrite? Gradual refactor? Introduce new languages within the company or stick with what people know? Educate people about paradigms which might be more suitable, but which will feel unfamiliar? What leads to a better product, someone who is experienced with PHP, or someone just learning to use Typescript?

All that theoretical knowledge about superior paradigms won't help you now -- No clean slates! You have to build a skyscraper city to replace a swamp village while keeping the economy running, together with builders who have no clue what concrete even looks like. You might think "I'll throw my superior engineering against this, no harm done if it doesn't stick", but 9 out of 10 times that will just end in a mix of concrete rubble, corpses and mud.

I think I'm somewhere between 2 and 3.

I think I have most of the important knowledge about a wide array of languages, technologies and architectures.

I think I know how to come to a conclusion about what to use in which scenario -- most of the time.

But dealing with a giant legacy mess, transforming things into something better, without creating an ugly amalgamation of old and new systems blended together into an even bigger abomination? Nah, I don't think I'm fully there yet.

C# Collection class had me pulling my hair out for hours the past two days.

With a list, you can do new List<T>(IEnumerable<T>) and it creates a new list with the contents of the parameter in it.

With new Collection<T>(ICollection<T>), however, the new object is a reference to the parameter passed in.

Is it just me, or does that seem fucking bonkers?

Watch an "Introduction" video about it, or read the docs/blogs on why and where to use this particular tech. If you find it useful, then get your head down and work. Watch every YouTube video, read company docs, read random blogs, read FAQs. Honestly, any source you can get your hands on.
And never forget to write more code than you read.
Consistency and hard work is the only key.
I still remember when I was first getting introduced to front end, I didn't sleep for 3 straight days and was studying all that I could.