I went to your web site & saw that it was Japanese, a language I don't speak. But I got up the courage to hunt around there anyway. I hope I didn't open myself up to being bombarded with spam E-mails. I picked this video at random:https://jable.tv/videos/jul-820/
Without launching playback on the web page, VDH saw this:
I downloaded the highlighted variant. I took these next 2 screenshots at about the same time. The first one shows the VDH download status menu you get from clicking the blue dot at the bottom of the VDH menu. The second one shows my Resource Monitor during the download.
This last image shows one of the few really scientific ways to talk about download speed: the Windows Resource Monitor. You need to provide something comparable before we can properly discuss what kind of download speeds you are getting. You'll note that here the CoApp is getting about 2.5 million bytes per second of line usage. But I want to point out the small graph in the upper right corner of the Resource Monitor. It has a marked sawtooth profile. This is the sort of thing I typically see on YouTube. It indicates that the web site is throttling their downloads. They allow you to get a short burst, maybe 2 seconds, of very high speed data transmission, then they stop the connection for 1 or 2 seconds. So maybe they were sending me data at 15 or 20 million bytes per second for a second or two, and then they were sending me nothing at all for a second or two. The way the Resource Monitor measures line performance is it calculates an AVERAGE level of data transmission over the trailing 60 seconds. So even though the speed was oscillating wildly between a lot & nothing at all, it averaged out to about 2.5 million bytes per second. That's actually pretty decent, as these things go. YouTube barely gives me 400,000 bytes per second, and regularly as low as 200,000 bytes per second, a truly horrible speed. So this site is giving me service I cannot complain about in the slightest. You can expect this sort of thing on a site that might have a lot of users trying to download things at any given moment. This is their way of continuing to supply an acceptable level of performance to the largest number of users. They can't afford to give download speeds of 10 million bytes per second to 1,000 users at the same time. So they do what is reasonable with a reasonable amount of server power.
Subtracting the file creation time from the time of last modification, you can see (in this next image) that this one took 13 minutes to download. I feel that is reasonable. Certainly fast enough that if I were to get 5 like this one, it might take an hour at most, certainly not the 5 hours you were seeing. Here's my results:
Here's the file properties as reported by Windows:
Not the greatest resolution but not the worst, either. The bit rates are a bit low but you can expect this on a free porn repository. Pornhub is about the same. It's about trading off quality for file size. Just for yucks, here's what ffprobe had to say about it:
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Q:\VDH Testing\Japanese porno.mp4':
major_brand : isom
minor_version : 512
Duration: 01:59:19.04, start: 0.000000, bitrate: 1399 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 1262 kb/s, 29.97 fps, 29.97 tbr, 90k tbn (default)
handler_name : VideoHandler
vendor_id : 
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 127 kb/s (default)
handler_name : VideoHandler
vendor_id : 
Here's how VLC saw it:
And here's a totally G-rated moment as VLC showed it:
I didn't sit & watch the whole 2 hours of it. I just skimmed it, sampling it at intervals of about 5 minutes, just to make sure it had video & audio all the way to the end.
I should point out that having or not having a VDH license has no impact whatsoever on the download speed. VDH downloads at the exact same speed regardless of whether you have a license. The impact of a license occurs after the download completes. You can read all about that over here:https://groups.google.com/g/video-downloadhelper-q-and-a/c/BzPLK2YyL-s
Look for the reference to the VDH license, click through to that, & read what's there.
Here's an example of what you should have posted as part of your initial problem description:
I'm on Windows 7 64-bit, Firefox 96.0 64-bit, licensed VDH 7.6.3a1 beta, CoApp 1.6.3, VLC 3.0.16 Vetinari.
You should tell us that information about your setup. You should also post something like what I have shown as my Resource Monitor display. If you're on Windows, you have Resource Monitor because it is part of the operating system. If you're on another platform, I can't say what you should be using. I have no experience with those systems so I don't know what tools they have for displaying this information. But I have to believe such tools do exist. You need to show us what that tool says while your downloads are in progress. Then we can have an intelligent conversation about your download speed. My experience here shows that neither the serving web site jable.tv
nor VDH itself causes any sort of slow speed of downloads. We need to get a more complete description of what you are doing in order to pinpoint your problem.