It's unlikely Python is to blame for that, unless they implemented something very CPU bound in it. I wrote wxPython apps in 2000 or so and they were very responsive.
It is likely a combo of Python + someone not good at using Python with networking. When working with anything that talks a lot over networks you need to use threads or separate processes to keep things feeling responsive during network delays. Python doesn't make this easy, so lots of devs skip it and it makes the programs feel sluggish.
Hmm, that might make sense on a server, but this is talking about a GUI client. Also, Python has trouble with CPU-bound threads but not those IO-bound.
