I agree with you. My teacher has an Avantgrand N3, and it has the heaviest keys I have ever played on. No that it is a bad thing, but it takes time each session to get used to it.
I have no experience with the Yamaha C series, but my teacher tells me that the weight is similar. Students that train on AGs have little to no adaptation effort when playing on a C7 at the recital. On the other hand, I do have experience with the U1 upright and I find the keys on the N3 to be heavier (although no that much).
AG are great instruments. It seems that they force you to develop good habits, so to speak, both in terms of touch and voicing. On my digital Roland FP 7-F via Pianoteq, the melody and contrasts are much simpler to emphasize. This makes my playing "lazy" on other pianos, where I need to make the melody sing much more. The AGs do not have, in my opinion, such shortcomings. I would much prefer mastering my pieces on the AG than on my current DP.