I love C3 but here's what I think about this subject.
C3 has sacrificed a lot of structure over the years for the sake of quick development which makes a lot of pros of the engine harder to sell than they should actually be. A lot of fundamentally important features aren't fully fledged, actively work against each other or have an inappropriate / non-existent UI (imo hierarchies, containers, families are a glaring example for this).
Right now you can observe a lot of Godot newcomers finding out about its (amazing) node system and being thoroughly impressed. In contrast, showing the way hierarchies are handled in Construct to an experienced dev will usually lead to a very negative reaction.
This is just my observation, i'm not claiming that this is the biggest factor or even a big factor in the marketability of C3 overall because that's a very complex subject. I have immense respect for what the C3 team has achieved so far.