I think Ritchie will very likely be better than Newhook and Jost.
But the Avs need to make some moves and they don't have the luxury of making someone like Ritchie off limits.
If they can bring in a better stylistic fit at 2C than Mitts, there's much less need for Ritchie. It's also not clear if he'll be a center or wing in the NHL. Also, not totally clear what level he'll play at, or how long it will take to get to develop into a playoff impact player. That's the level they need out of their top 9 the next couple years.
If the Avs need to use Ritchie to bring in a D man like Jones, and can still swap Mitts for a better stylistic fit under contract a couple years or more, I think you make those moves.
If they decide to keep Mitts, then I think you keep Ritchie for insurance next year. But it's probably a notably worse team for their Cup run this year, and they may be stuck in the same position next year.