Perhaps there are routers that don't handle well large amounts of data, but from my experience what typically is happening are two things:

1. the fairness in TCP is done per TCP connection, bittorrent opens many connections so they take over the whole bandwidth. You can limit number of connections or throttle the bandwidth used by BT (of course you will get slower speeds), maybe there are some other ways.

2. when you maximize your throughput ACKs might get dropped which slows everything down (I suspect that might be the issue you're talking about) again you could throttle or enable traffic shaping and give highest priority to ACKs. This worked well for me.

3. Bufferbloat. It's still a thing. dslreports has a bufferbloat score, one of my coworkers has been really impacted by it. http://www.dslreports.com/speedtest

I heard about bufferbloat, but I didn't think it was related to bittorrent maximizing throughput

It depends: packet loss due to bitorrent is a problem, but low loss and high latency makes it dramatically worse, and that is the bufferbloat cast. If you have 1-30 second pings (or I've seen even worse), when doing torrents or other heavy outbound traffic, it falls apart.

Even 1 second is already pretty severe bufferbloat, let alone 30 seconds. Your latency should increase by under 25-125ms even with upstream and downstream both running flat out.

But all this can be adjusted with concepts like pining, rate limiting, queuing, connection limits, even geo-fencing. I would gladly share % of my server's unlimited transfer to give back a tiny range of Debian or DockerHub packages which I have dowloaded and use. And I don't want to mirror the entire distros, which is condition to become an official host of distro mirror.

> In a lot of the world, upload speeds are very limited and ISPs charge an arm and a leg if you exceed your upstream data caps.

Not all 1st world countries have data caps. I pay ~20$ for month for 37mbps (15 upload) with no data caps (it's literally the cheapest plan I could find, if there was cheaper available, I would take it).

in Russia i have a ~$15 plan 1gbps (~700 realistically)up/down unfortunately it's clear that ISPs are not going to be able to upgrade their hardware nor keep prices low due to government interventions, government controlled ISPs competetion, mandated DPI censorship(paid by ISPs) so very soon internet in Russia will be as shitty as in most western countries that lack competition

P.S. until 2009-2014 russian internet was completely out of government sight. an average internet user in big cities had a choice of 3-10 ISPs competing prices etc

With LPD, we could have two PCs upload to each other, it would be even beneficial to ISPs if everyone didn't have to download updates at a similar time from the furthest-away server. Especially in developing countries.