Having dabbled with Tidal in the Model S with premium audio today, including pre-downloading albums I’m super familiar with whilst on wi-fi, I came to the conclusion that if I had chosen Tidal as my primary source of music it was totally fine and easy to use but regarding quality, there just isn't enough in it, if anything at all to make me want to have it alongside Apple Music lossless and the Apple ecosystem, neither in the house or the basic Spotify with premium connectivity in the car.
Is that not to be expected?
Tidal as implemented on the car appears to only support HiFi quality at best, ie CD quality (44.1k/16). So comparing it against another lossless format, or a CD source should give parity. It sounds like that has what been achieved. Job done. It would have been a different story had you made the argument of Tidal Master quality (on equipment designed to play at a higher quality of what Master can offer vs Apple lossless, but even then, not all masters are better than 'CD' quality. What Tesla Master quality allows is higher than CD quality material to be streamed, but as it appears not to be supported in the car, then Tidal HiFi = CD = Apple Lossless (at source) = xxx CD Lossless, no better and should be no worse although no experience of how well Apple Lossless would transfer in car. Hence my earlier comment that Tidal HiFi is the tier that would suit most, unless playing at home or, adding this one in, wanting to contribute a bit more to the originators of the music.
Ironically, 'CD' quality has been available in car for decades, the step forward should not be commenting on quality (even if much of the industry did take a backward step on quality vs convenience), but on bringing CD quality and convenience and instant access to a huge library of material, rather than having a 6 CD changer or scrabbling on the floor to grab the next CD to play.
Now, whether high resolution (ie better than CD quality) would be discernible in the car environment is rather a moot subject, although in car FLACs at 96/24 (twice the resolution of CD) will play.
However, this all detracts from the true question of, does Tidal offer better quality than Spotify when played in the car? I don't know as I don't use Spotify, but all I know is that the in car Tidal offers a better interface than accessing my USB/FLAC media at same quality with a much larger library that is easy to access. Job done as far as I am concerned, but then I have been a Tidal subscriber for many years so I have no financial comparison to consider. But for those who already have committed to another service, or might want have start paying for material, or swap provider, then a different conclusion may be made.
For some, having access to high resolution material, ie better than CD quality, or in the case of Tidal Masters, at the quality of the original Master, Tidal offers that in a streaming format over the internet/WAN with modest bandwidth requirements. That level of quality is available in download/file/LAN often from material from unknown province (ie a lot of high resolution material is simply 'CD' quality that has been up sampled - nothing wrong with that if done properly, but up sampling can be performed very well by many pieces of kit so it is not necessary to sell it at premium as hi resolution) but what Tidal Masters does is bring parity at that level. And that allows access to a huge catalogue of material for those that want the best out of their equipment, but for those that don't, there are other solutions, but very few equals.