I am generally not a mecha fan, Gundam included, but I've wound up seeing some Gundam works that have genuinely impressed me and stuck with me; right now I'd say that my two top works are The 08th MS Team and War in the Pocket. For reasons that don't fit in the margins of this entry I recently wound up thinking about how important the presence of Gundams is in those two shows. Could you take the mobile suits out and replace them with something else without fundamentally damaging or changing those shows?

(This question makes more sense for me than for a Gundam fan, because what I like about these shows has almost nothing to do with the Gundams in them.)

I think that The 08th MS Team is actually surprisingly dependent on mobile suits in specific, because to make the whole feel of the show work you need a specific combination of attributes in your military machinery. They have to be ground based, because it very much matters that the MS Team is down there slogging along in the mud instead of flying distantly over it all. They have to be single pilot, because the whole dynamics of the situation would change if the pilots (especially Shiro) were working in a close team with other people in their vehicle instead of being alone. And they have to be powerful because people react to this; things would feel very different if the team was using, say, armed motorcycles instead of something that dominates the battlefield.

(That they dominate the battlefield also gives the MS team's actions special weight and their position special importance.)

War in the Pocket is a more ambivalent case. A lot of the situation and impact are not particularly dependent on mobile suits in specific so it feels like you should be able to swap them out for something else, but at the same time it's hard to figure out any alternative that leads to the crucial final confrontation while keeping Al so involved in it. To keep him so involved in the confrontation you probably have to keep it on the ground, so once again you need ground-based military machinery that has a single pilot and is sufficiently scary to force the defenders to sortie expensive and rare experimental hardware instead of relying on standard military vehicles and forces.

(Of course the background and settings for both shows are completely entangled in the Gundam Universal Century mythos as it is. But I think you could contrive some relatively similar setting that removed the mobile suits. After all, mobile suits are arguably an analogy for aircraft in the first place, although if we take this too far we wind up saying that the Federation is the US and Zeon is Japan in World War II.)