I'll say that after an hour or so of keeping this powered and/or having actual video on the screen, it seems brighter than initially.
With the exception of maybe 15min total about five-years-ago, and another 15min many years prior, I hadn't turned on the monitor in about two-decades. At this point I'm so use to high resolution monitors/phones/TVs, that maybe this monitor is actually normal.
The brightness knob on the front is turned up all the way though. Video games seem decent, but the main text screen seems dim. In any case, it's going back into the storage box and plan to use a TV in the future.
Ah yes, the old G2 voltage. I forgot much of the terminology, however, monitor repair was a very short lived career for me, so I didn't have time to absorb much except the flyback voltage can sneak under the boot and zap your wrist when turning the yoke after installing a new tube.
Something I have learned is if you rejuve it and get some improvement you should quit while you're ahead because hitting it again will often set you back worse than when you started.
You basically hit the nail on the head from the experiences I remember. Rejuvenating a CRT was taught as common practice until someone approached me saying it's either not effective and/or short lived.
As for measuring voltages, that's good input. I immediately went with an aged CRT due to the age of the monitor. For all I know, this probably has leaking caps too, so maybe either now or sometime in the future I'll take time to remove the cover. For now, I'm just happy to have one more project behind me (repairing my old C64).