I'd agree with regards to scrying spells, but am not so sure when it comes to seeing the future. A mysterious yet inevitably accurate prophecy works very well in literature. Handled well and used sparingly, it might even be an effective part of a D&D campaign, but I just don't see it working with the requisite frequency and reliability to build an effective class around. I do think the subclass is well put together considering those constraints, though, so I'll hold off on downvoting it this time around.
I have looked into the future and your transmutation didn't work.
Portent is the ability most able to change a high level villain into an non-threat. They fail their save or receive a crit. A lucky diviner with a simulacrum is even better. The DM never gets a good roll.