I looked up the first and last submission IDs in August 2020 on both FA and Weasyl, to find out how many things get posted on each site. I collected the data today, October 10, 2020.
On FA, the first submission ID on 1 August was 37,513,120 , and the last submission ID on 31 August was 38,011,321 . That makes 498,202 submission IDs in 31 days.
This is an average of about 669 per hour; 16,070 per day; 112,500 per week; 492,200 per month; 5,882,000 per year.
On Weasyl, the first submission ID on 1 August was 1,931,541 , and the last submission ID on 31 August was 1,941,737. That makes 10,197 submission IDs in 31 days.
This is an average of about 14 per hour; 329 per day; 2,300 per week; 10,200 per month; 120,400 per year.
In August 2020, FA got about 49 times as many submissions as Weasyl.
FA got about 26% more submissions in August 2020, compared to August 2019.
Weasyl got about 14% fewer submissions in August 2020, compared to August 2019.
Caveats and disclaimers:
The raw submission ID count doesn't consider deleted submissions. Some critters will post a "now streaming" or "YCH reminder" submission and then delete it within a day or so; this drives up the submission IDs, but doesn't lead to more content on the site, long-term.
I don't have data on any other furry art sites, or "general" art sites like DeviantArt, because I pretty much don't use them.
I mostly don't upload artwork; I just favorite and comment.
Data was gathered manually with Deer-Spangle's FAExport API (forked from Erra Boothale, see https://faexport.spangle.org.uk/docs ) and Weasyl's built-in API (documentation previously at https://projects.weasyl.com/weasylapi/ , but that site no longer responds; I used an old copy from http://web.archive.org/web/20141016173921/https://projects.weasyl.com/weasylapi/ ).
I am not associated with FA, Weasyl, or any other furry art site, as a staff member, moderator, programmer, or anything else.