As someone on the other side of this - applications sink to the bottom and often never receive a response when sent to places like jobs@, so LinkedIn is a way to at least get the attention of a real person.
I’d suggest calling out on your job posting that LinkedIn messages may be missed and the email is the correct place to reach out.
Merely anecdotal but my worst experiences over the last year have been with startupschool companies - not saying they’re all bad (maybe I’ve been meeting the statistical minority that aren’t great) but as a part of the community I really expected better
Depends on the use case but all physical resources are finite in some limit so you may want to distribute that load so the different domain processes can scale appropriately. When/where/how is dependent on the application you’re building.