When you have barely the upstream bandwidth to send the ACK stream of your downloads, anything sending something becomes a big burden on your system.

Not everyone has the luxury of fully symmetric internet connections even in this age. Yes, my uplink speeds are absurd when compared to a decade ago, but when I ratio it to my downlink, it's still slow.

I have no comment on residential proxies. Somebody doing something in my name is unacceptable to put it very mildly.