I agree completely.
New players should be encouraged to play in Modern but I don't think Gladiator cards should be completely banned from Modern ranked though. I think a more gradual approach would be better.
Modern League:
Bronze- ALL SB cards are banned
Silver- Gladiator cards are banned
Gold- Gladiator cards can be fielded vs. other accounts that have Gladiator cards
Diamond and Champs- Wide Open
P.S. Modern is a really frustrating experience. Facing unbeatable teams time after time after time and knowing that you can't even rent cards that would allow you to compete is... well, I quit and went to Wild and I'm not a new player.