If I had even just one, plus the ability to play it, I’d never searched for a guitar plugin, but I’d rather used an audio-midi interface to play along with the other instruments I don’t have/I am unable to play
I really don’t understand why you risk losing a high manual ability that you reached studying and practising a lot 
As far as I got, you can do it only with sample-base plugins, but at the cost to have precooked loops, exactly like precooked MIDIs
That is by accident at the base of one reasoning of mine
And this is why I started using EZBass manually
But playing a bass with a keyboard is easier than a guitar
And you are thinking to substitute a physical sax with a plugin, you are in more trouble 
Fair question.
I suppose it’s a bit like the reason why, despite I have well over 1000 DVD and Blu Ray movies, I instead sit on my sofa with a remote control, scouring the streaming channels hoping that “there’s something worth watching” - despite I could just walk downstairs! And yes, I have movies still in the shrink wrap!
I don’t see myself as losing a skill but as acquiring new ones. An exchange perhaps?
And I’m not sure that the world of digital audio is really one where one can master everything? As such, I’m more interested in mixing and mastering than I am recording.
Remote control are the humankind ruin 
Kill the remote control, and you’live a better life
sure.
But listening to music is a psycho-acoustic experience. We end up “hearing” what our brain constructs for us. Therefore if the overall result of my combining a bunch of tracks into a song, and someone comes away thinking “wow, love that sax solo!” to me it becomes immediately immaterial where the sound came from.
Personally I find it useful to find some happy middle ground between what’s “real” and what is generated. It’s all about the final impression.
I don’t think it’s true that having a sample-based VST ties one to loops. I know you don’t like NI and Kontakt, but that’s certainly my experience that they do a brilliant job of sample libraries, and which give us a completely open and non-constrained instrument.
A sample is a sample…
If the sample has a “scratch” in certain places, you cannot remove them or move them elsewhere in the loop, unless you split the sound and restitch it, but this is a huge job that keeps you far away from Mix & Max
The MIDI can be easily edited, but I find it boring in the long time
Playing all instruments with a little help instead is funny, but YMMV
give us a completely open and non-constrained instrument.
If you mean guitar libraries, only if you are very able at keyboards…
Otherwise, you are in a very boring cramped cage
So, friendly advice could be to test before buying, but you cannot with NI
I use scaler for a lot of music but actually find using EZ keys as a controller for UJam product far more productive and easier
Midi out from Ezkeys into Ujam
I’m a guitarist of 40 years and with a little tweaking on the Ez editor setting up Logic to raise the key range and adjusting the midi by nudging midi and optimising chords on grid ! I don’t have any issue with UJam (2) products?
So perfect results.
So Back to this after a littler research to see what problems you are having … Use scaler to find your chords - drag these directly either in bandmate or onto grid.
Using EZkeys as controller for UJam midi out - You can select any Chords (Any) Maj Min 7th Add 9 ! I have not found a single chord you cannot use in UJam ! so that doesn’t seem to be an issue
As with all of these midi through midi driven products you will have to set up and use the Grid Editor at some time to get the right chord or key, this is so simple in EZ - there is an Octave feature and also Chord Inversion included in the Circle of 5ths also a function for sparced chords and Melody/ostenato.
You can adjust the chord blocks in EZkeys to create new Patterns ! ( so the lack of patterns in Ujam) doesn’t apply - use single phrases in the ‘common patches’ and build your own. ! or mix and match with UJam
Maybe as an experienced Logic user and guitarist is may seem a little easier for me to work out
I have tried NI ( still have mint )and several other Guitars based VSTs with a seemingly more open architecture but what I found is I end up spending hours trying to build patterns and midi in the VST and wasting time in complicated confused interfaces… just to have to alter the midi then again in Logic
EZ products are you friends with Scaler as a midi in and chord construction superb !
Yes, I use The Toontrack trio when I want a fast base to jam on
nevertheless, I cannot avoid putting Scaler in the formula, because it helps me with solos using keys-lock sometimes, or having Scaler suggest me the possible matching scales that I recreate in Ableton Live