I can only speak for myself when it comes to download speed but I haven't noticed any issues with itch.io in that regard during the last few days - neither from personal experience nor through the forums, which would have a lot more complaints if the problem was more wide-spread. In this day and age upload speed and download speed are usually asynchronous, so having a bad download speed while your upload speed is through the roof sadly isn't much of an indicator for anything either (besides maybe overheating).
If I were in your situation I would try these things in the order listed:
1) If you live with other people, politely ask if their machines (PC, phones, consoles, streaming to a TV, etc.) are currently using the internet to receive meaningful amounts of data.
2) Check if your machine is currently downloading any automatic updates you forgot you enabled. (A quick way to check your traffic would be your operating systems network monitor.)3) Request a new IP from my internet service provider (it can't hurt). This can be done with very few clicks from your router's menu and shouldn't take longer than a few seconds. Alternatively, disconnecting your router from the power grid for 30 seconds to 2 minutes should have the same effect.
4) Call your internet service provider's hotline and politely requests that they look into the issue. In the end, it's their job to take care of those issues, because you pay their company for it. (If they ask, you always need that bandwidth for work related reasons. Not that they would check, but itch.io hosts a wide variety of things.)
As for the delay in the response from itch.io: As far as I can tell they have been swamped by users with various complaints related to the enormous size and popularity of the Bundle for Racial Justice and Equality. Justified or not, this (together with people complaining about things they could have found in the FAQ) creates a huge amount of backlog. (I'm not trying to cast shade on you, btw. Waiting for 7 days is more than twice the patience than I've seen in most other posts.)