First: Welcome to the forums!
If I understand correctly, you are doing backups then backup copy jobs to local storage and then GFS tape archiving. Am I correct?
Personally, I would go for backups to local storage (for x amount of time, I will come back to that one) and the backup to tape for offsite archiving (or any other air-gapped solution).
You state that you keep 3 months. Think of it for yourself: Every time you had to do a restore, what was the date of the data you needed to retrieve. If we use statistics, we see that way over 90 percent of the restores comes from the last 7 days, most of the rest from the last 2 to 4 weeks.
If you talk to your C-level, explain them that 4 weeks onsite (on disk) is probably enough, and that you can move the rest offsite. But do explain also that it means that RTO for the first 4 weeks is good, and after that... not so good. If they agree with that SLA. You have saved probably the storage you need
My thoughts on this