Hello Maxdimitrio,
first of all nobody calls me Mr. Archut, just Oliver is fine..
You point out a very interesting issues triode vs. pentode in triode connection.
The V41 as well as other V and U series pre amps, the triode connection is due to the tube limitation, only EF12 and 14 were issued by the "Reichs Rundfunk" so in order get rid of gain for an additional buffer stage, they choose the triode connection. The later V76 works in the same place with a very high negative feedback... and an even more special tube than the EF804S the E83F.
There are several times in tube history that a mesh or grid anode surfaced, first in the 1920 to get a better tube performance.
This is a kind of related and Barhausens Handbook of the Vaccumtube suggest a frequency depended character of a grid or mesh triode.
In HF application there is a use for that type of tube, to reduce internal capacitance, but in audio it is hard to quantify.
I did several test of in production mesh anode triodes vs. american and german made NI or P2 solid anode triodes, each time the solid ones worked better, maybe because they were made better.
For some people it is a matter of believe, but here are some ways for you to test and measure.
Did you ever only used the 2nd grid of the pentode as anode? (plate and 2nd grid to ground)
Also did you ever hooked up a beam power tetrode or pentode, were the 3rd grid or beam former are hooked up to the cathode inside the envelop? You might want to try that.
As pointed out that germany is the land of special purpose tubes, some of them have gold plated pins, but most of them were deigned for HF use.
Best regards,