I completely agree. We currently have a customer with a Hyper-V host with over 1TB of data. It takes 4-6 days to push a full backup to the cloud. We are struggling to come up with a good solution, as missing that many days of incremental backups is not viable. We previously used Solarwinds Backup, which syncs the local backup to the cloud in the background. If CBB could implement a similar feature, it would be great!

The concept of a periodic full is what confused me in the beginning. I assumed it was like tape backup - a whole new full backup of every file. But if a file never changes, it never gets backed up again. Think pdf's, jpg's, mp3, etc. Our "Full" is run once per month and takes only a little longer than an incremental as it is only uploading full copies of any files that have changed since the last Full backup.
We have many customers with >1 TB of data. We do file level incremental backups of the changed data to the cloud nightly. Typically the monthly "full" on 1TB is only about 30 - 50GB. We run it on weekends and it finishes with no problem.
We also do VHDx file backups to the cloud each weekend for DR purposes. We have separate Hyper-V guests for the Domain controller, File server, SQL app, etc. Further, we use different vhdx files File server instance C: (OS) drive and the D: (data) drive so we only need to upload the C: Drive VHdx which is under 30GB (compressed).
One of our customers has 4TB of data , and once the initial upload was done (that took a long time), we have had no issues completing incremental backups to two cloud locations each night as well as a local backup and weekly VHDx backups.
There is no need to do a VHDx backup of the Data drive as you have the file backups to pull from.
And if your setup has apps and data on the HyperV host, then an image backup can be done the same way, just exclude the data paths.
I apologize if I am misinterpreting your situation, but would be glad to assist you in any way that can.