What is the fastest way to upload and/or transfer large video files to and from a client?

I do editing work, that basically has me downloading several GB of raw video files (.mov), plus several other "B-Roll" video files, as well as a lot of photos etc.

I complete a daily project for my main client where he sends me the aforementioned files... I edit it all together, and then I upload it back to him.

He sends it all to me in one .zip package that he uploads to his Google Drive account, and sends me a link. The .zip file he sends me is approx. ~2 GB in size every time. When I am finished with my edits. I have a single 1.5-2 GB .mp4 file.

I have been sending it back to him simply by uploading this file to my Google drive and sending him a link to it... just the same as he does.

However... his upload time for the 2 GB .zip file seems to be NOTHING compared to my return upload. Even through the file I upload is almost the exact same size... sometimes it takes 11 min. to upload... but sometimes 6 hours!!!!

It usually takes approx. ~45 min. He, my client... is always chirping about how long it takes for my uploads to become available for him to download the end project. I upgraded my cable to the biggest and fastest internet speeds available... and I live in a metro city... and I have the most popular (Xfinity) ISP.

I've done all the upload/download speed tests, and I do not have some kind of "problem with my internet."

But I still just cannot imagine why this guy's able to upload a 2 GB .mov file in a couple of minutes... while my exact same size file takes me 5-10x longer to upload.

I've tried using iCloud instead of Google Drive. I also tried another service called Mega. Mega... was the fastest... but out was STILL nothing as fas as my client's upload speeds.

Is there some better/faster/more professional way that I can look into? It would have to be a very user friendly method... as my client is not up for a lot of change, and if I had to try to teach him about ftp or using FileZilla or anything like that... I think it would cause his head to burst.

What do you guys think is the "industry standard" way to reliably and quickly send finished .mp4 files of 1080p video to a client?