TFK ECC83s are so "legendary" for their "tonal richness"
No they are not.
Exact opposite - in the Marantz 7 circuit they are fast, reasonably transparent and very flat. I have a draw full of premium flat plate Telefunkins. They have never sounded rich.
If you want rich - Mullards tend to be much more fullsome the expense of speed and neutrality.
The problem with any discussion on tubes is that the best tube can be circuit related - you can't make blanket statements.
I like Telefunkens, but, I never considered them to be tonally rich sounding tubes. The ones I heard were very lively and dynamic sounding, but, considerably leaner than the likes of Mullard and Amperex.
Absolutely correct - I have drawer fulls of flat plate telefunkens - they are as described. I also have a stash of Mullard CV4004 and M8137's both are richer and fuller sounding than the Tele's.
In my Marantz 7 I preferred the Telfunkens.
In my Jadis preamp I preferred the Mullards in some positions ( but not all ).