I have both the FE55 and ZM50/1.5 and there's definitely room in the bag for both of them, though I haven't been carrying both at the same time. The FE55 is very predictably good throughout the range, but I personally prefer the look of the Sonnar from 1.5-2.8. I was trying to figure out why, as when zoomed in the FE55 bokeh is really smooth compared to the Sonnar, even with the Sonnar at f/1.7 to take the edge off of the rings. For me, it comes down to the round vs. cat's eye shape at the periphery. I'm just not a huge fan of the swirly look, and the Sonnar is one of the few bokeh character lenses I find appealing. Different strokes I guess.
My wife and I spent a couple weeks in Spain, and my kit usually boiled down to either the A7II with a FE16-35 and FE55, or the A7m (Kolari vII) with the ZM25/2.8, ZM35/2.8, and ZM50/1.5. The AF combo is easy to shoot and the lenses have pretty predictable performance across the frame, best at f/5.6-8. The ZM's are tricky even with the mod, but I have to say that at the pixel level, carefully focused, the ZM25/35 combo is visibly better than the zoom, and I have a pretty good 16-35 copy even at 35mm.
I need to do a side-by-side of the ZM50 on A7m and FE55 on A7II, as I wonder if the ZM50 is giving up a bit with the unmodified sensor. However for evening photos, I carried the ZM50 on the A7II to take advantage of the IBIS and keep my shutter speeds up, and I was happy with mid to long distance "moody" shots from f/1.7-2.8 at night as long as I cropped to 4x5. The corners of the frame can indeed get ugly with this lens until well stopped down, and even then it can't touch the FE55.