> We're on 400Mbps, and even then I manage to block internet for others when I download a large file at full speed.
That's more of a router/QoS issue. A large download shouldn't negatively affect quality for other uses, especially VoIP. If the place you're downloading from has a pipe bigger than yours and can saturate your bandwidth you're going to need to implement some kind of rate-limiting/queue management.
I've seen a lot of people complaining that their 100M+ connections are "slow" for that reason, and they upgrade to 1G and they complain again. It's not like they're doing much on that 1G line either, just say a Steam game download at full speed followed with a stuttering Zoom call. You'll be surprised how far you can push a 10M DSL connection with good QOS (assuming you don't have multiple users streaming video and such).
That's more of a router/QoS issue. A large download shouldn't negatively affect quality for other uses, especially VoIP. If the place you're downloading from has a pipe bigger than yours and can saturate your bandwidth you're going to need to implement some kind of rate-limiting/queue management.