The solution will move faster than is necessary, and may cause surge marks.
No, it won't. This would mean that everything developed e.g. in a Jobo would come out uneven. It would mean that everything developed in a dip & dunk system with nitrogen agitation would come out uneven. It's not the case, evidently. The cause of agitation-related uneveness is due to unevenness in the actual flow patterns, most notably very turbulent flows along some part of the film surface and more laminar flows in other parts.
It's very visible e.g. on the older Jobo 2509 non-N reels in a 2500 tank and rotary agitation where the part of the film that touches the reel tends to exhibit these surge marks due to turbulence in those areas, while the center section of the sheet that's far away from any reels tends to be exposed to more laminar flow patterns.
Similar effects can be seen in a Paterson tank with a Mod54 holder where the 'fingers' of the holder create turbulence (much like the vortices emanating from the wingtips of an airplane) while the rest of the film is not exposed to these effects. The solution here is not to increase fluid levels or to reduce agitation, but to increase the frequency of agitation and to ensure that the agitation motion is brisk enough to expose the entire film to turbulent flow patterns. Additionally, adjustments to reel geometry may be necessary, such as in the case of Jobo adding the flaps to their 2509N reels.
I would be inclined to believe that more film is over-agitated
There's no such thing as 'over-agitated' film. The issue is uneven flow patterns.