I am certainly not going to say anyone is wrong here as I haven't tried it. What I can say is that total derailleur "throw" is generally much larger than what gets used once limit screws are set properly so this is not the issue (though it would be more so if using a triple crank where indexing needs to hit that middle ring correctly). For doubles you merely shift up, and you shift down, and the limit screws set where the derailleur movement ends.
The 11sp cassettes have closer set cogs and narrower spaces between cogs which must be compensated for by a narrower 11 sp chain. Thus the front cranks then get slightly redesigned to also work best with that narrower chain.
Important here is the fact that one can generally run a narrower higher speed chain on a wider, older lower speed group (but not vice versa) because the inside spacing of the chain is the same, just the outside width has to be narrower (and less durable) to fit between narrower spaces between cogs and rings on a higher speed group. For example, I run 9sp chains on my vintage 6sp Pinarello, but if I ran a 6sp chain on my 10sp Campy equipped Look, the chain wouldn't even fit between the cogs, let alone shift well.
All of the above arguments are saying that a 10sp chain will hang up in an 11 speed crankset but an 11 speed chain WILL work and should work fine on your 10sp groupo too.
All of that said, I run a Campy Chorus 10 speed groupo with a Shimano 10sp compact crank and 10sp KMC chain on a CX bike with no issues whatsoever. Fact is, most front derailleurs and left brifters don't know or care what speed group or even what brands you are using and intermixing. Its chain compatibility that matters most. I bet I could set up a 9sp shimano front derailleur to work fine on my Campy group simply by adjusting the limit screws and trim appropriately. Derailleur design and throw hasn't changed much in 30 years. CX'ers have regularly run 10sp Campy brifters with 9sp Shimano derailleurs because the Campy brifters are more durable and the Shimano 9sp derailleurs are cheap. In fact I just picked up a 7400 series Shimano 9sp DA front derailleur and some Campy Record 10 brifters and will be running that with my 10sp Shimano compact crank so I am mixing both speeds and brands up front! The key point is that you will likely need an 11sp chain to get best performance with a new 11 speed crank. Lastly, Campy used to tell you that you needed a special Campy derailleur designed to work only with Campy compact cranks. This appears not to be actually true since my standard Campy derailleur works fine even on a Shimano compact crank!