Besides the reasons stated above I don't have any strong objections to disabling the auto muting and soloing from the synth audio track. The feature pre-dates quick grouping and was a handy way to quickly mute/solo all related synth MIDI tracks without needing to hunt them down. It was what people wanted at the time.
The code for synth mute and solo is centralized fortunately so changing it is not difficult, however I need to discuss this internally and also make sure that there are no side effects to changing this behavior in case something else relies on this functionality.

Thanks Noel for looking into this, much appreciated!

As an option cool.. Thanks.

I just changed this. No its NOT an option, I just removed the old behavior by removing the case 1 and 2 below for mute and solo.
 
Mute "smart grouping" rules to mute logically related synth tracks
1. If a synth audio track is muted, mute all its MIDI track siblings
2. If a synth audio track is unmuted, unmute all its MIDI track siblings
3. If a MIDI track is muted, mute its associated audio track only if all other sibling MIDI tracks for the associated audio track are muted.
4. If a MIDI track is unmuted, unmute its associated audio track

Solo "smart grouping" rules to solo logically related synth tracks

1. If a synth audio track is soloed, solo all its MIDI track siblings
2. If a synth audio track is unsoloed, unsolo all its MIDI track siblings, if no related audio tracks are soloed.
3. If a MIDI track is soloed, solo its associated audio track
4. If a MIDI track is unsoloed, unsolo its associated audio track only if no other sibling MIDI tracks for the associated audio track are soloed.
 

Noel, excellent! Thanks.

OK thanks..

I'm sorry but I have to retract one part of that fix. I can't remove rules 1 and 2 for the solo case. There was a good reason for those.
 
The reason is this:
If you solo just the synth audio track without soloing the synth MIDI track you will hear silence. That would be confusing and unacceptable behavior. The synth audio and MIDI tracks need to be soloed together, so I need to retain the rules 1 & 2 for solo.
 
Hopefully I don't find anything that prevents the mute case :(

Noel, it seems a simple fix would be to keep any MIDI track unmuted if it's synth audio track is soloed.
 
BTW, it seems if you are unlinking the MIDI mutes from the synth audio tracks, would MIDI tracks not stay unmuted anyway if you solo another MIDI/audio track? So why would you ever need to mute any MIDI tracks regardless of whether one is muting a synth audio track or soloing any other synth audio track.
 
Put another way: If you only ever mute synth audio tracks during mute/solo operations on synth audio tracks, why would the solo case stop working at all? No MIDI tracks would ever get muted unless you specifically mute a MIDI track itself.
 
Put yet another way: Mute/solo operations on synth audio tracks should not change the mute state of any MIDI tracks.

The way I read it, if the synth's audio and MIDI tracks are completely unlinked, then soloing the audio track will not solo its MIDI tracks so there's nothing feeding that audio track because only it is solo'd.  However, if you mute the audio track then it doesn't matter if anything is or is not feeding that audio track - it's muted.   At least I think I have that right... 
 
BTW, great discussion, very interesting.
 

CakeAlexS
Problem with that is a performance monitor would also be a resource hog so again it would need to be an option in preferences. Nice idea though.

I was being sort of "blue sky," thinking of when DAWs would start to get some AI happening