Generally speaking, lemmy is much more cpu bound than it is bound by bandwidth - so the added bytes don’t matter that much. The example above was just for 1 community. Now imagine the user is subscribed to a dozen communities, but doesn’t even browse lemmy that day. That’s probably thousands of api calls made to keep his server on sync, and 0 requests saved.
Like the big instances have literallyhundreds of thousands of workers running in order to get all the updates out. If one of those calls fails, it gets put back into the queue for retry.
OP asked if having his server added to the lemmiverse would alleviate the load “Like with torrent”. That is demonstrably not the case - it only adds more workload on the other servers, with a break even point that’s highly variable. Yes, your server will be nice and snappy, but the origin servers have to pay the price - death by a thousand papercuts synchronisation calls.