The Eico loudness switch "problem" was a problem for everybody except Eico. Eico intentionally designed the loudness circuit in all of their models so that there was a major volume reduction when the loudness circuit was engaged, since they believed that -- if used properly -- the loudness circuit would only be used during very low volume listening occasions, such as for the purposes of providing background music. Of course, that is in fact supposed to be the true intended use of any loudness function on audio equipment. Eico took that definition quite seriously though, and designed their loudness circuits to actually address the intended goal: When engaged, the volume level was significantly lowered (allowing much more low volume level flexibility with the level control), and the low frequencies were appropriately boosted -- exactly what you need to appropriately adjust the unit for low level background type listening.
The trouble is, nobody else took the definition of the loudness function as literally as Eico did, so that virtually everybody else made their design simply boost the lows (and usually the highs as well) as long as the level control was somewhere below about a 12 noon setting -- and had it all happen without a significantly change in volume level as the loudness circuit was engaged or deactivated. Against that, the Eico loudness approach -- although well intentioned, and even more in keeping with the intended used of such circuits -- simply came off as strange, weird, poorly designed, containing schematic errors, and a whole host of other accusations about what a problem it was -- but all as judged against the "norm" of other manufacturer's loudness circuit designs of course.
In the end, well intentioned as the design was, it was simply never accepted by the public, with virtually everyone today agreeing that -- for various reasons -- the circuit needs to be "fixed". To that end, I agree -- if only because today's vacuum tube audio enthusiast hardly use their prized piece of equipment to provide low level Muzak type background music, but rather, operates the equipment when they really want to LISTEN to the music, relegating a cheap boombox for actual background ambiance. Also, the idea "low level listening" by vacuum tube audio enthusiasts today likely represents a significantly higher (although still considered as low) listening level (as in foreground music) than what Eico was considering low level listening to be back in the day.
So, for a number of reasons, the circuit does need to be "fixed" today. However, the Eico engineers should be given some slack, as in fact, they were the ones who technically got it more right than anybody else did. In their mind (correctly), the equipment was high fidelity equipment, which was defined by one term in the day: accuracy. If you were running the equipment at "normal" listening levels, the loudness circuit was not supposed to be used in those occasions. If you did, it wasn't accurate, so they designed their equipment so that it basically didn't work at normal listening levels.
Of course today, the idea of strict accuracy has taken such a rear seat to everybody's own subjective definition of what the term means, so as to have basically fallen off the bus. Therefore, in today's listening environment, anything goes, which means if the loudness switch doesn't work at high volume levels, then it obviously needs to be "fixed". If any of them are still around, I'd sure hate to be the poor Eico engineer who designed those circuits!
Dave