Agreed There is, however one aspect of flight where lack of diherdral makes a noticeable difference in speed & that is the case of inverted flight with flat-bottomed wings.

If you take a typical trainer -- like a Hobbico Superstar, with an OS .40 LA, & fly inverted, it can maintain level flight but will barely be able to climb. The reason is that the flat bottomed wing, plus the dihedral, requires a large AOA to develop sufficient lift for flight, which creates so much induced drag that there is virtually no reserve power for inverted climb. If you take the dihedral out of the wing & fly inverted again, the aircraft flies noticeably more quickly & can actually develop a modest rate of climb -- because the lift vector is now vertical, making all of the lift available for flight, thus reducing the AOA & some of the linduced drag. This is enough to increase speed sufficiently for inverted climb.

This isn't theory -- I've done this with several trainers & the effects are quite evident.