Ramos has never been a great catcher, only average/serviceable. He lived on potential and injuries the first couple of years, but why would anyone expect him to "bounce back" from a season like last year? That's just what he is.
Among other reasons, because average players often bounce back from seasons where they struggle?
His Steamer projection is for 1.7 WAR in 400 PA, with offense very similar to 2014 but obviously well below his best seasons. That sounds just about right to me.
Lucroy is projected at 2.7 WAR in 520 PA, which I think is a little pessimistic.
Obviously these are projections, and Ramos could suck while Lucroy is an MVP candidate. I'm just pointing out that in believing that, you are choosing to make assumptions and not believe the likeliest outcome.
The likeliest outcome in my mind is that Lucroy is 1-1.5 WAR better than Ramos each season over the next 2 seasons. Is that worth paying a king's ransom in prospects for?