Man that's a tricky analog circuits problem I'm struggling to answer appropriately. My first instinct is to say, no cathode heaters are meant to be isolated in all cases. Then I was thinking they're arguing for a (B+) coupled to the heater circuit instead of a ground. So heaters would be -(B+) relative to cathodes (in all other tubes) instead of 0 (assuming standard anode coupled load).

However since the cathode of the rectifier is going to be at a higher potential relative to all other cathodes in circuit, I could see how that might be an issue? but I still can't see how coupling heater circuit to B+ makes a better option.

> Not only that, but the DC voltage is divided by inherent resistance of the heaters, so really only half of B+ sits on the heaters.

That doesn't really add up to me since there should be no current flow, therefor no voltage drop.