Will the 23mm cannon kill anything besides planes and soft gvs?
Tanks with little to moderate top like the Panzer IV, M4, Panther or the German tank destroyers can still be killed even with the 23mm. Actually, for a long time a 23mm equipped was the only tank busting option this game had beside the Hurricane D (which about nobody used). Tanks like the T-34 series or Tigers are going to be very difficult or virtually impossible to kill, though. (Back in the day, I picked up the Hurri D as my mainstay because it was the only way to cope with T-34s and Tigers without ords.)
Another general word. Killing tanks with tankbusters is a bit as shooting down bombers at high altitudes, inasmuch as players frequently fail for the same reason: Impatience.
You gotta take your time to setup your attack properly. It actually doesn't take that long at all, but in reality you often see players flying straight and level and low from the field to a (spotted) tank and trying to kill it by shooting into it's face. And then screaming bloody murder because they have been maingunned