Once upon a time, when photos were manually guided, the rule of thumb was that the guide scope should be approximately 1/2 the focal length of the imaging scope. With the way guide software integrates star centers That's no longer necessary. But think about it. The higher the magnification the better the resolution and the finer the guiding.
My 14" Meade mounts a $119 Orion 80mm f/11.3 guidescope (91mm focal length) And paired with an ASI 174MM guiding is pretty darned good. This scope is no longer sold by Orion but there are a couple of identical scopes available. The scope only weighs 3#. And part of the beauty of this scope is that it's long enough that it mounts with 2 inexpensive ScopeStuff rings fastened to the castings at either end of the 14". No heavy dovetail needed.
Yes, very small very short scopes are being used for guiding. But I believe that a longer focal length still provides greater sensitivity when it comes to guiding..