I think before linkedin people were doing this with email and phone. Literally cold calling your old coworkers. Not sure linkedin really created anything that didn’t exist previously especially if you live in some major hub of industry as you indicate.

It did make it easier though. I don't have to keep a list of potentially outdated phone numbers and email adresses. LinkedIn makes it much simpler to broadcast your availability.

Most of LinkedIn is just garbage though, especially if you somehow connected with social-media people or marketing people. Marketing people on LinkedIn are weird, they can't form coherent sentences and they can't even sell themselves.

You could strip down LinkedIn down to your resume, availability status and your email address and it would be fine.