Thanks for the detailed report — you found a real bug, and it’s now fixed.
What was happening: Your global flags were being passed to rclone, but when you copy a folder in the file browser, RcloneView was sending its own per-operation config that included transfers=4 (the internal default). In rclone, that per-call value overrides the global --transfers you set, so your --transfers 16 (and --checkers 32) were being silently ignored for drag-and-drop
copy/move/upload/download. That’s why you always saw exactly 4.
The fix: Ad-hoc file-browser operations (copy/move/upload/download/rename of folders) no longer inject those defaults, so your global --transfers, --checkers, etc. now take effect. Saved/scheduled jobs are unchanged — those still use the per-job settings in the job dialog.