I used Virion pretty much the entire way through my first playthrough. He was very useful early on as the only ranged physical attacker, and then by the time I'd hit the second half of the game, he'd seen so much use that he was taking zero damage from enemy units walking up to him and meleeing him.
Benched him on my second playthrough, and honestly, it hasn't made much of a difference at all. So archers/snipers are take or leave for me, I suppose.
Bow users are saviors in Lunatic+. They can completely negate counters and be able to dodge attacks reliably because of their speed. Just finished CH. 12 on L+ classic with my sniper tanking all the knights. My MU had to unequip her weapon and hide in the corner while the sniper took them down one by one. In Lunatic and lower difficulties, bow users are rarely needed.