Meh, very weak. Perspective and reflection can both easily explain the phenomenon. His attempt to debunk perspective had him holding up a cell phone with a light clearly above it (on a lamp pole) without the necessary perspective. Nor does light merely reflect off of oceans, but the entire surface of the earth reflects it, causing what's known as earth shine.
Finally, when planes are flying level, they actually fly with a one to two degree nose up deck or fuselage angle. And are the videos he's showing of planes during their ascent or descent? That's the time you're most likely to see planes.
Extremely inconclusive.
Perhaps he can address the engineer who used CAD to demonstrate that if the sun were setting behind the curvature of the earth we should see a shadow on the bottom of the clouds as it sets, from one end of the horizon to the other ... but that never happens.
He also strawmans the FE argument about the boats disappearing over the horizon. Eventually they will disappear whether the earth is flat or globe simply due to the convergence with the horizon, waves, atmosphere, etc. But experiments have repeatedly proven that ships can SEEM to disappear bottom up over the horizon but then can be brought back into view by zooming in. So the appearance of the phenomenon is largely due to the limits of our eyesight, which can be overcome with the right optics. Again, the FEs often take precise measurements to demonstrate that these boats should be hidden by the geometric horizon but can be seen anyway.