How does wood hardness affect the sound of a TT on a wood TT platform?

The wood in a plinth of turntables has much more influence for example than the wood used for making table tennis rackets.
Have you ever tried to use table tennis rackets with identical rubber but different woods?

I have been trying for a long time and there are macroscopic differences.
I believe that for the plinths the same thing is the same, the problem is that nobody has ever built plinths with different woods and then made tests and measurements with laboratory instruments.

So few of the geniuses above provide any practical, REAL, scientific insight into what Janka Scale hardness might be best for TT isolation.  Why don't you just say you're not certain rather than bloviating about what might work?

What is a fundamental to what is desirable as an inherent property for a Plinth or Isolation Platform - Sub Plinth for materials selected is the following:

Damping Factor ( The materials ability to harness received energy or at the other end of the scale bounce it back to the source. Preferably a High Damping Coefficient for an Audio Support ancillary used within a System).

Dissipation Factor (Speed at which energy within the material is lost or no longer significant as a reading)

Most who have a HiFi System and have the opportunity to make change, seemingly reject the materials available today that are much more fit for purpose to perform a particular role and maintain materials that are very poor and wanting for the role selected.

Do a search on “damping factor wood types”, there are some studies on the subject. 

One does not need to search too hard to discover a Board produced as a

'Phenolic Resin Impregnated Densified Wood'  

is the material where the the Damping and Dissipation Properties are very attractive to be used in a Audio Set Up.

Today it is quite easy to find, TT Plinths, Sub Plinths, Tonearm Wands, Headshells, Speaker Baffles or Full Cabinets and even Chassis and Bespoke Component Casings are being produced from material with the properties of Branded Board Material.

Most of the annual volume of Phenolic Resin Impregnated Densified Wood on the market consists of resin-impregnated densified veneer products, while solid resinimpregnated timber boards are rare. Some example of names or tradenames of densified material, some of them not existing anymore, are: Bakelisiertes Holz, Carbonwood, Compreg, Delignit, Delignit-Feinholz, Dehonit, Hydulignum, Insulam, Insulcul, Jablo, Jabroc, jicwood, Kunstharzschichtholz, Lignofol (Preβschichtholz), Lignostone (Preβvollholz), MyWood2, obo-Festholz, Panzerholz (Delignit), Permawood, Permali, Pregwood, Ranprex, Sonowood, Staypak, Surendra, Transformerwood, and VANyCARE.

Typical products made from this type of densified wood are storage containers for liquid natural gas and associated support structures, wear plates for machinery and transportation vehicles, machine-pattern moulds, tooling, jigs, bulletproof barriers, security panels, transformer parts, neutron shielding, audio.

Picawood is not in the above list, this is a board produced with increased plies of veneer to the typical production methods where up to 25 Boards are compressed to produce a 1" (25mm) board.

It is typically a guidance to use Cross Grain Ply Board  @ 25 Plies per 1" (25mm).  

I would really like to see a Three x Orientation for the Plies, but when discussing with an individual has a direct communication with a manufacturer, the batch to be produced was quite substantial, way beyond a Group Buy quantity and the Wastage as a result of the orientation laminations was to be quite substantial as well.  

Kaiser Speakers has a bespoke board produced using similar to the Three Orientation design, to improve on the already impressive Dissipation properties of Cross Grain.