Hi,
I would concur to some of the comments.
A key frame in H264 is already encoded in a similar way as JPEG. Major differences are the "defaults": the flexibility of JPEG in terms of colors depth, color map, but that can be also addressed with a video codec, too.
Then when using a video codec like H264, it will also contain differential frames which will only send differences. It depends on the content but these frames can be significantly smaller than a key frame, like 10x.
So the math is that H264 can nearly only be better than JPEG, assuming proper parameters for the type of content, the targeted transmission challenges, the transmission type.
Using JPEG is close to using only key frames from a compression stand point (not to say, it is exactly like that), which is close to older protocols like MPEG-1 (DVD), or close to intra-frames only codec (like used as intermediate formats, for editing or preservation). And the difference in size is a no-brainer, eventually this is the amount of data that needs to be sent to every user.
In my opinion, the first consequence of using JPEG only is the cost per device, the number of concurrent streams from a server and what not.
If the perception of quality is low with H264 compared to JPEG, some parameters need to be adjusted.
And ultimately, H264 is already an old codec anyway, not the one I would recommend, newer ones can address visual perception and bandwidth in a much better way. the VP-8/9/AV1 family will reduce the "macro block" effect of the H.26x codecs.
Using HDR will dramatically improve the quality and will crush any benefit from JPEG, benefits related to the number of bits per pixels and the poor 8bits color maps, with a much higher efficiency.
Should the volume of users and the cost per user be of any consideration, a lossy video codec will prevail.
Video projects are challenging in the details: wish you the best.