If you're directly wired, know your modem is capable of 1 gig, and no one else is using your network (i.e. downloading large files) and you've tried various speed tests throughout the day (e.g. early morning, mid afternoon, night, weekend, weekday) and it's all around 630 then that would seem to be an ISP issue. Did you try different servers as well? Speedtest.net, fast.com, etc? Just because the game server might not be able to push 1 gig doesn't mean your network connection is limited there.
But yeah, if all that is good and you're still capped at 630, then that seems like maybe it's the best your ISP can do. If there's a 500 Gbps plan that is significantly cheaper, perhaps that would be worth downgrading to. I guess that just depends on how much you need the speed, how tight money is, etc. 630 is still REALLY good though, like top 1-5% of all ISP speeds in the US. The average US ISP speed is 42.86 Mbps (as of Feb 2021). The fastest state is NY iwth 138 Mbps. So like I said, 630 is still extremely good. Perhaps just buy a bigger hard drive/external hard drive/NAS/etc? That seems the simplest and best solution. You don't want to have to redownload the same game 100 times anyway...