The hd 540 is THE vintage headphone. If you want to buy a very good headphone and not spend much then I think you will be happy with it, although a good amp will help
Ive had a few others from around the same period such as HD400, HD414 - They all have similar sounds. Essentially smooth and often quite equal across all frequencies
although in a sense I feel anything special is kind of held back - there is no crystal clear highs, no thunderous bass and the mids are really nice
They all are really nice easy to listen to headphones that Im happy to have in my collection
Compared to the HD540 though . . . they are good
but the HD540 are spectacular. One of the best reference headphones ever made. Myself and others actually prefer them to the modern HD800S
They have a natural, human quality that is sadly lacking in modern headphones. They make the music sound like how is was played.
Anyway, it may well be as you say BUT bear in mind the brightness, more bass and fuller mids will in no way be 'better' than the HD540's
They are still are a really good headphone and in many ways outperform modern headphones. In some cases, maybe not technically but listenaly
Go for it
Ps: Its difficult to say if your statement is true because it depends very much on your source and amp and the condition / suitability of the pads.
I have certain combinations of high end headphone and amp that sound 'meh'..ok BUT then using a cheaper mp3 player with a cheaper amp
and they sound spectacular...o_0
Just something to bear in mind