Naim introduce a turntable - the Solstice Special Edition

The plodding sound of high mass turntables (I have owned an AMG and a Kuzma) really seems contrary to the Naim philosophy

Its not the high mass, it is the design and implementation.
I have heard both the TT's you mention - the ploddy sound has nothing to do with mass, the rubber belts and weasel motors are the primary issue.

The ARO was certainly an ergonomic challenge. But my real objection was that it sounded awful - thin, lightweight, no bass. 

Thats not my experience.
I own several arms including Aro/Dynavector/FR64S plus many others.
In a direct comparison using the same cartridge on both the Aro & Dynavector there was no lack of bass from the Aro. Dynavector was tighter in the bass, but the Aro went as low and remained tuneful ( good timing ).

I would be looking elsewhere in your system for the thin sound. What I do know of the Aro ( I've owned it for over 20 years ) is that I beleive it has a narrow operating range with regard to compliance & tracking weight. High compliant cartridges and very low compliant cartridges with long cantilevers tend to be less compatible with the Aro.

My Aro has been set up with a custom tonearm lift and on the fly VTA via thumbwheel.

Should anyone question the motivation for my response to Lewm, the answer is here "Your little experiment". So f-ing condescending I could just...... Well, you get the idea.

@fsonicsmith
Well after the red mist subsides, @lewm s point is correct.
Just because you had a poor result with a heavy platter on your 301 does not mean a heavy platter cannot work with other setups.

I have built both Garrard 301’s and 401’s and in fact the heavy platter options are different for each model On my 301 I use a modified original platter, heavier platters upset the bass timing. Conversely on the 401 I built increasing the platter to a 11kg brass platter improved pitch stability.

I have both a 301 and reference high mass TT with 26kg platter.
It is the high mass turntable that has speed and coherence the Garrard 301 ( nor anything else I’ve heard apart from the DD Technics SP10mk3 but that has other issues ) cannot match.

Platter mass has to be viewed in context with the capability of the drive system and how that mass is managed in terms of stored energy.

Dynamics and tone are certainly important characteristics of a reproductive system but timing is solely up to the musicians. 

That may be correct in terms of the music, but not necessarily playback. The reality is that if you have phase or frequency response aberrations in a system, it can easily alter your perception of timing when listening, or at least mask the "intent" of the musician.

Example - the other night I was sorting out some records and found Jazz at the Pawnshop on Propius - hadn't played it for many years so I put it on. The changes in tempo of the individual instruments for example are easily heard along with the interactions between the players - in a system with phase or frequency errors these attributes can be ameliorated or even lost.

Turntables are a lot more than just a time machine - they provide a foundation for the arm & cartridge to accurately track the groove. It is a base for a mechanical measurement system. Why do you think sensitive measuring instruments in laboratories are often placed on isolated antivibration platforms.

If you cant hear differences between turntables with the same arm/cartridge then just get youself a Technics 1200/Shure V15 and you are good to go. But that does't mean other people cant hear differences.