Designers -who's been around the longest ?

Any designer will do. Sorry to hear about the V-FETs. The bigger problem is what John Curl has been saying -HQ parts are not produced in good numbers anymore.

The exception are the new GaN-FETs-but these are output-only devices. MSB makes a terrific resistor-DAC but this is only one co.

John Curl has been around and active for a LONG time. He is correct about high quality parts.

It’s easier and cheaper for large quantity FET manufacturers to skip a few steps in production (especially baking time) to produce chips that still meet specs. But those specs don’t necessarily carry over to quiet / low noise audio components. And the quantities of chips required for high-end audio manufacturing doesn’t justify the added expense in manufacturing.

Keith Herron has also been around for a long time, since the 70s. He designed Crate and Ampeg musical instrument electronics before forming Herron Audio.

William Johnson of audio research fame and Sid Smith of Marantz fame  must  be considered.

Kenneth Stevens of cat can't  should not be overlooked.
He has continued to improve his  products and they must be reckoned with in the marketplace 

Unlike curl, pass and Tim, who are legendary designers, ken built and builds products that are arguably state of the art.

You have to be both a great engineer and know all the audiophile tricks to produce a great sounding product-and he knows them all.

For all of curls, tim’s and pass’s greatness I have never felt they produced a great sounding product that I had to have.

Nelson is essentially a one trick pony, Frank van Alstine never reached the same legendary status. Bob Carver is extremely capable. I have not heard one of his tube amps but I did once own a Fuzz Linear 700 which was a very good sounding amp in it's day and very affordable.
John Curl can design anything, from sound boards to phono stages, Concert sound systems to preamps. He has been involved with the design of some of the most highly regarded high end equipment and he is not finished yet. If John Curl's name is on it, you can bet on it being a great peace of equipment.