He has improved the loading times, yes, but it's not an engine created by him, he has used rempy, does that justify the long waiting time for the update, no, it doesn't help much that you have erased 85% of the game, some new things he has added to Jenny's story, but I think he could have incorporated them perfectly without the use of the new engine. It probably sounds very fanciful, but the best thing would be for him to continue his development of the game with the old engine and with intervals of time to release updates in the new version, it seems to me that he has enough money to be able to have a second team transferring the content quickly to the new engine.
If you can't understand a damn thing it's the translator's fault, and my bad writing xd