I have fished for trout exclusively for the past 6-7 years with light weight Spey rods. They have many advantages over the conventional single hand 5wt.
I do on occasion fish dry flies where yes, the SH is superior.
Wet flies and soft hackles are a pleasure to fish with the Trout Spey rods,, this is about line control and presentation.
Larger heavy flies cast with ease compared to SH rods.
Quick change heads from Scandi to Skagit when needed to dredge a deeper pool or run.
Longer casts into the wind,,, no comparison.
High stick or Euro nynphing,,, easily done with the longer rod,, the Spey rod longer handle and reel position make the rod more neutral balance and is less tiring WRT the single hand rods of 10ft+.
If you only fish small dry flies,,, get the 5wt, or preferably a 3wt/4wt, for all other methods the Spey rod is far superior.