For an iPad2, I was able to solve this issue for my son.
His iPad was never used on a cell network and he never knew that it even had a SIM card in it.
I popped out the SIM and connected to iTunes.
It activated straight away.
It appears that IF it has any SIM installed, in Apple's infinite wisdom, you're forced to activate over the cell network and disregard any other connection method. Seems like some of those millennial programmers they have on staff need to learn how to write better conditional statements and error handling in their code. Pretty pathetic if you ask me.