Can you become a good network designer if you have not had exposure to routing&switching troubleshooting or implementation experience? For example, imagine you have only VPN, remote access, load balancers and wireless experience and generic knowledge of network topology. Do you think through training in network design and jumping direct to a network architect role one can become a good network architect?
I've been in many fields, not only IT. I meet designer both fresh graduate from school, years of working as designer but no hands-on/field experience, and those with years of hands-on experience. In comparison, those with hands-on/field experience perform better many times than those with no hands-on/field experience.
There is a big difference between the book, class room classes, and lab scenarios from hands-on/field experience.
You will probably get a number of different views on this but i'll offer mine from own personal experience.
My current job is as a Network Architect responsible for the LAN/WAN design and some of the network security. Prior to that i had a few years experience in administering, troubleshooting switched/routed networks.
I wouldn't want to claim i was good or bad, that's really for others to say, but what i would say is to design something the more you understand from experience how it actually works the better. There is a world of difference between reading about something and actually having hands on experience with it and sometimes i have only really truly understood something after having to set it up, no matter how many times i read it.
As a designer you need to be aware of what technologies are currently available, what they can do and just as important what they can't do and how these technologies can be intergrated into the infrastructure you are working with.
You also have to work with some of the less technical aspects such as budgets, business requirements etc. which as an engineer you might not have had much exposure to.
As a side note, in the company where i work the designers are also expected to be a kind of 4th level support so it does help if you have done the config stuff before but that could just be the way my company works.
I'm not trying to discourage you. If you have a good understanding of switching/routing concepts then there is no reason you could not progress in this field but i would strongly recommend that keeping your technical skills sharp is a huge bonus no matter which direction you go, engineering or designing.