@Tom.
No. Not really. If you check a datasheet for EL-84´s we routinely run them way way way pass what is reasonable. Spec calls for 300V maximum for g2.
Modern day n era tubes in turn are NOT what they used to be. Hence why lowering voltage for g2 is a good idea.
What´s more a mere fact is that a lower power amp will spend more of its life at wide open throttle,or close to it,then a more powerful amp. What the zeners bring in that case is an amp that at all times lets the anodes/plates take the load and therefore will stand up to going full blast days at end.
What the zeners do primarily,from a practical point of view,is change the g2 nodes reference and thus change the powertubes manner in which it handles transients.
In short the zeners will bring you an entire powerstage that is more "snappy" and willing to comply.
100 Ohms vs g2 in turn isn´t primarily to protect the screens. It is for EMI/RFI protection.