The photo unfortunately doesn't show the shadowing effect you refer to, but your verbal description offers a valuable clue. If you set the cutoff with the brightness turned up to maximum, and the brightness was still insufficient after the adjustment, then it is quite likely that the crt itself is the trouble. I've seen very few truly worn-out Mac CRTs (screen burn is much more common), but I have encountered a couple.
If it bothers you enough that you don't mind a small risk of killing this CRT, here's a final test: Disassemble the unit and remove the connector from the base of the tube. Connect a 15V DC regulated supply across pins 3 and 4 (the filament), and let that overvoltage cook the CRT for a good 5-15 minutes. In many cases, this will recondition the surface of the cathode (at least temporarily) and restore emission. Reassemble and test. If the ghosting goes away (or at least goes down signficantly), and brightness increases, then that pretty much seals the diagnosis.
If it bothers you enough that you don't mind a small risk of killing this CRT, here's a final test: Disassemble the unit and remove the connector from the base of the tube. Connect a 15V DC regulated supply across pins 3 and 4 (the filament), and let that overvoltage cook the CRT for a good 5-15 minutes. In many cases, this will recondition the surface of the cathode (at least temporarily) and restore emission. Reassemble and test. If the ghosting goes away (or at least goes down signficantly), and brightness increases, then that pretty much seals the diagnosis.