This is definitely not a fair argument to make. Obviously, each side dismisses some of the other side's beliefs about how the universe works. From the perspective of either side, the other side sounds less coherent because a lot of the things that one side says will make no sense in the context of the other's scientific belief.
For example, from an RE perspective, universal acceleration and the various "gravitation" forces are an incoherent attempt at fixing a deeply flawed hypothesis: the Earth is flat. The amount of correction is so mind-boggling that it's like overfitting a machine learning model; while the hypothesis may eventually explain all current observations (with IMHO a ton of corrections that FE people haven't yet fleshed out), it continually needs fixing because it has no predictive power.
Yet, and I disclaim that I cannot speak well for FE, on the other side, things like gravity make no sense to them because, well, it's just an observed force that causes masses to attract each other; there's really not a good explanation of how it exists via the mediator particles found in the Standard Model. To them, the argument of a sphere being locally flat is a rationalization of the observation that the area around us is flat. They don't see physics as Round Earth people do; sometimes, even stuff like Newton's laws has been questioned. It doesn't help that the horizon is almost flat, that accelerometers read 0 in freefall, rockets are hard to get into space, and that generally modern science is a very complex thing.
I should note that while modern science is a very complex thing, it is so far the simplest explanation that scientists can find for a plethora of observations and experiments, many of which FE is unfamiliar with (but then again, that's the opinion of a Round Earther).