A better ADC (like in virtually any outboard audio interface) certainly doesn't hurt and would definitely be advisable for musicians, but it's far from necessary for a youtuber / home office use case.
My experience is that a high-end device like MixPre II is fine with a dynamic mic. Focusrite or Tascam US needs a cloudlifter to get enough (clean) gain. Random stuff like BlueYeti is hopeless with crackling noise.
So maybe you don't need a great ADC but you have to choose your audio interface very carefully (for its preamp.)
Typical interfaces have a fine ADC and some kind of pre, but the pre might be noisier than desired when paired with an unusually low-output microphone, so if you already have an ADC via motherboard line input then you "just" need a pre. I don't mean to lump all dynamic mics into this problematic low-output category (SM58 is much higher output than SM7B, both are dynamic) but we could certainly say that condenser mics should never be in this category when a few inches from someone's face.
Why are mics like the SM7b better than mics like the MV7 or elgato one that just work over usb? I don’t understand how they actually work or why all the extra equipment (audio interface, gain booster, cables) is worth it - what’s the tradeoff being made when you use USB?
It's like asking what makes a VM better for a website when I could just use a SaaS site builder. Use whatever works; depending on your goals you might end up with the exact same finished product.
Getting super high end with microphones is only really applicable in the music industry IMO.
Fun fact: Michael Jackson recorded the vocals for Thriller on an SM7B.