My questions seems to have revealed, that the CPU load you mention at best can be the load you have on a single thread and absolute is'nt the load you have on your total CPU.
You don't answer my question about your specific CPU model, but i then assume your CPU use hyperthreading so your 6 cores can handle 12 threads.
A simplyfied example. Lets say you have a CPU with 2 cores that handles 2 threads, and you have one synth that put 50% load on one core, and you have another synth that use multiple cores so it in example actually is able to put 25% on both cores, then both actually will put the same 25% load on your total CPU, even if the singlethreaded synth on the meters - that you apparantly look at - will look like it use twice the power, even though it does'nt.
So if you in example take all your examples, then you will not be able to read a load that's the sum of the numbers you mention, in a meter that only show the load of the most stressed thread or core. The total CPU load will be much less than the sum.
Your statement about how many instances you can manage, unless perhaps if you have some power settings or other settings that's wrong, or you have defects of some kind somewhere, unless your new MAC and CPU is worse than your old.
In generel it look like you compare apples against bananas.
I also assume you have'nt used some U-he synths like Diva, NI's new Massive X that use a lot more total CPU power than the old Massive, or used xfer Serum, some Tone2 synths like Icarus or Synapse synths.
They all can use a lot of total CPU power.
Saying your other synth does't use as much CPU power does'nt say anything, except something about you don't mind comparing apples and bananas.
To me your example picks look like you actually have much less CPU load on older Arturia applications, as you clearly have picked some that's not light and that's not among the oldest.
Your informations seems to be aimed to draw a bad picture, and not aimed to troubleshoot.
It's actually no secret that Buchla V is heavy on the CPU. You can read that on Buchla Vs sales site. And if you in example could use 4-6 instaces of that before, then you should do better now, if you have a better MAC and better CPU.
I can also say, that i also find the brand new OB-Xa, that's btw is not in the V-Collection yet, can be heavy on the CPU when many voices is playing, and if you in example have a 16 voice setting. I doubt you used that one on your old MAC.
Matrix 12 is not the lightest on CPU, but it's not very heavy either, and i actually think your numbers verify that.
You also should be able to run more instances of this on your new MAC, if it's better than the old.
Good emulation will not be as light on the CPU as very old applications was and is.
I can add that i on my 2012 laptop with a 2012 i7 model 3610qm - 2,3 GHz, 4 core 8 thread apparantly can run much more, than you say you can, when usig 48000 Hz samplerate and 256 samples buffer like you with my internal standard soundcard and using the examples you mention, and my Ableton live 10 lite.
I can't compare your CPUs performance with my laptops and desktops CPU, as you have'nt given me the model name i asked for.
But i would believe you should have the possibility of much better performance than my laptop.
(Btw - the only question i've asked twice was one you did'nt answer the first time i asked.)
I do think some Arturia synths could benefit of having quality settings, and be able to be multicore applications. Only Piano V has a multicore option. Just keep in mind, that a multicore possibility would not give less total load on the CPU. As it is now, then you only have the samplerate and buffer settings for quality settings, and that's not useful.
Also Arturia (and other manufactors) hopefully can optimize the CPU usage for those of the applications that use much CPU.
OB-Xa might even be more optimized, when it get it's first update. Othervise it really need to be multicore, to be able to play 16 voices on other than the a CPUs that have absolute top singlecore performance. Luckily it's easy to change the max amount of used voices, so lowering the voice number where it's possible can reduce the CPU load. Sometimes it may even give a better result on sounds that have a long release time.
Keep in mind that any voice in it's release fase count as a played voice. I'm btw not sure you have taking that into account in your examples.