Maybe the Captain is not as confident in your abilities as you are.
I have no issue with an FO, one who I know I can trust, disconnecting the auto pilot in the right conditions. I have seen one too many FO's disconnecting the AP and completely f***k it up. Flying the line is no place for show boating, especially in busy airspace. If you want your kicks flying go and hire a Cessna for the weekend.
I happily let them fly manually, try some raw data without F/D, fly a REAL visual without that monkey LNAV/VNAV stuff and definitely don't fly max ALT because I could not care less about fuel saving and prefer have a little margin in case of turbulence.
If I don't like what the F/O is doing I can give advise as we fly along and maybe he can learn something, if I still don't like what he does I can take over and as a last resort I can do a G/A because there is a "no blame policy".
At the end of the day the F/O and myself have had the opportunity to refresh our skills and maybe even improve them making us a more proficient crew if compared to those sop monkeys who are lost if you switch off the F/D on them.
And to those who bring up the "busy airspace" thing I remind you that, apart from literally a couple of airports, we fly to little ****e holes in the middle of nowhere while our DL or UA colleagues fly visuals into ORD.....