This is news to me. I wasn’t explicitly aware that the Roman military did not employ massed archery formations in warfare.
That said, I am reasonably certain that had the Roman military chosen to employ archers en masse up to including mounted archers, they would have been highly proficient. I have no doubt that Roman military archers would be highly trained and very capable. The Romans excelled in whatever skills they required their troops to master.
The bottom line is that massed archery formations apparently were not needed for Rome to win battle after battle. The Roman defeat at Carrhae cited in the video is the exception that proves the rule, demonstrating how pathetically rare enemy archers were able to defeat Roman armies.
Necessity is the mother of invention. There was no necessity for Roman armies to feature massed archery in their military strategy. If it ain’t broke, don’t fix it.
I think Roman cavalry provided most of the support for the infantry.