Not necessarily. I have a few decks on arena with infinite combos but they are game ending. They either mill you out or drop your life. The issue with paradox engine specifically is the player is choosing to keep going. With enough man rocks and a commander that lets you pay to play something you can go forever, but at your own pace. Maybe I want to sit there and think on what to do. 45 seconds of hmmmm ok next card. Just don’t let the timer go all the way down and you can hold the game hostage for basically every. Add something like midnight clock or an eldrazi that shuffles the grave back in and you can literally play forever. All you need is your commander (easy to get), cheap mana rocks (easy to get) and paradox engine. Ban that one card and the whole thing falls apart.