It is like saying you find Lancashire too busy and overpopulated and you wouldn’t like to live there when you are basing your opinion on spending a day in the Arndale Centre
The Arndale centre is not in Lancashire. 
OP, I would not do it unless I had no choice. I moved there in my early 20s because DH had got a promotion there. It was the loneliest I’ve ever been. DH worked away often, I had no family down there, all the people I worked with had young families to get back to so couldn’t stay behind after work to socialise. We worked centrally but colleagues were scattered far and wide. You would have to think VERY carefully about what sort of people you’d be working with and whether the workplace would provide you with a good social life.
Commutes can be very long compared to living in other less crowded places where you can drive to work in 20 mins. When I moved to London It was autumn and I was commuting across the city and I didn’t see daylight during the week unless I Went outside at lunchtime. No exaggeration. That sort of lifestyle can become seriously depressing and claustrophobic if you’re used to an easy commute. I used to get in each evening just as Eastenders was finishing and think “blimey, I would have been home a couple of hours already back home up north”
Even nights out clubbing weren’t as good. Was a proper ball ache compared to a Liverpool night out. Couldn’t get a taxi,,night buses were erm, interesting. Back in Liverpool I would be home and in my bed much sooner.
I HATED the rush hour on the tube. It’s not just crowded. You literally have to shove people to actually get into a Carriage in the morning. Most people have a part of their body that is in the way of the doors closing or have someone else’s arm across their face, or,,worse,,a smelly armpit.
I gave up on the tube after a couple of years as I could no longer stand it (it WAS the northern line!). So then I just spent hours in standstill traffic on a bus. Very frustrating. But I got to read a lot of books and always got a seat so good in that way!
I love the countryside but I need to be in a city I think. But even London was too much for me. Jobs are easy to come by and there is a lot to do there. The downsides for me, like the cost of living/housing, and serious overcrowding everywhere and the pollution, and difficulties socialising made me move back up north. Still in a city but it’s much less claustrophobic.
I dont think London suits introverts terribly well!