Appreciate the replies, thanks all!
What kind of size images
The scans are mostly around 350-450MB. Uploading them unedited except for the front covers since I have a couple big boxes of CDs to do (hm, let’s see how many I can get done before I get distracted… ooh, a squirrel!), and for an archive raw seems ideal anyway. The files are a bit oversized since I’m scanning with a color guide (because of this other forum post) in case anyone wants to correct them later on.
A comparison between Google Images and MB\CAA upload is a little unfair on budget sizes
True… soz, wrote my last rant/post when I’d just lost my queued uploads for the nth time and was feeling more than a little “salty”. 
Just meant it seems to be struggling on the server end, not my own connection.
I think the most proactive thing to do, if you have a little bit of a tech brain, is to make tickets for improvements.
MBS-12524 Improve performance of cover art uploader
Yes, that MBS-12524 looks exactly like the issue I ran into! Those details look helpful.
I might play around with making a userscript. I’m not good at writing them like some of y’all are, but wonder if I could switch off the thumbnails that way. Potentially making it send more than one scan at once might help them go faster too. I’ll post back here if I can figure out anything.
Thanks all again 