There are a lot of ways to keep more deleted files, but none provide complete assurance that you'll have them all, short of keeping all backups for 1 year.
If you set Keep Backup for 1 year, you'd have everything. You can set the full to whatever schedule you want and calculate how many full backups that will be. Every 30 days would require up to 13 full backups in storage. Ever 2 months would require 7. Every 3, requires 5. etc.
I do not think you'll get lower storage use using GFS given your requirements of saving only a year. GFS benefits are geared to restore points and longer term storage, when needed. If you ran monthly fulls and kept only the last 30 days of backups and used 12 Monthly GFS backups, you'd have up to 60 days of fulls + Incrementals (2 fulls + incrementals for each) and monthly full backups for the remainder of the year. So about 12 monthly fulls + 60 days of incrementals.
If you kept only 3 Years of GFS backups (and no monthly backups) you'd have 60 days (2 fulls _+ incrementals) + 3 more fulls fulls for the yearly backups, but you'd only have deleted file restore capability for 30 - 60 days.
You do get the ability to use Immutability with Amazon S3, Wasabi, and soon Backblaze B2 with your GFS backups for added backup protection.
If GFS, Immutability, long-term retention management, large file counts, restore speed, etc. are most important, then use the new backup format.
But as I tell customers who are running file backups: If the legacy format and its version-based retention and file-level to cloud object management works better for you, then stick with the legacy format. If your primary concerns are deleted file restoration and reduced storage, then the legacy format may be a better fit. Do not be concerned about using the older format. It's tested, very capable, and if it's right for you, use it.