A1) Your typical mega corp that is too big to be one thing and filled with geniuses around every corner. So some parts are a pit and some parts aren't. It depends.

A2)Probably don't have to worry about it.

A 20 year old "startup"/feature factory where all the original talent left years ago and everyone in an IT management position has been with the company less than 6 years. The majority of developers(200+) here are hired fresh out of school, or only had 1 previous employer. Now the CEO spends all day courting the "institutional investors" so he can secure his retirement.

I've seen this in a couple of places. Junior dev assigned to design new system. Senior dev assigned to mentor junior dev. Senior dev encourages junior dev based on experience. Junior dev ignores everything senior dev says. Manager listens to whatever junior dev says and sidelines senior dev. Senior dev goes on vacation. System explodes.

At my company management often gives new stuff to interns while senior people are stuck with maintenance work. It’s really weird.

I've been at a mega-corp that let newly hired developers to build new stuff while senior devs are busy putting out customer fires that in many cases, were caused by those junior devs in the first place. "We want to make sure the junior devs have interesting things to work on so they stick around."

Not really. A new system means it is not in production yet, so if something goes wrong there is little impact. Breaking the working system doing maintenance can cause lots of problems, so it is seniors who are tasked with changing it.

Your manager should be called a practice lead and they should have recently been a senior dev. They should have been picked by other senior devs as the obvious choice since he’s the guy who spends more time on lunch and learns than writing code.