I completely agree with your statement that Senzel is not likely to have an impact (this year or next) because he doesn't have a position to play, unless an injury happens. He probably should be traded for "equal value" for something more useful to the Reds. He's not a plus defender in the OF and will probably never be. He might be a plus defender on the Infield, but he's blocked at 2b and 3b for a long time.
Seems like a waste of resources to put a top prospect in the supersub role. That is not a knock on Senzel, but he seems to be the definition of "Sell high".. His value is not going to increase as a supersub, it's only likely to go down. CF was a bad fit (especially with our poor defense in the OF corners), and still is. I understand why they did it last year. But this year's "plan" for Senzel is a bad one, unless I am missing something or another trade opens up playing time for him (or perhaps he becomes the full time LF and Winker/Ervin is pushed to the bench)
Even if the Reds plan on using Senzel as the starting LF, that is not maximizing his value.