Not really, it’s more mundane than that. For a long time only MIDI Tracks & Rack Instruments existed & to make them work together folks had to manually manage the routing & relationship between MIDI and Audio. Then Instrument Tracks were introduced to combine the MIDI & Audio into a single integrated Track type. Basically the advantage of Instrument over MIDI Tracks is they are simpler & easier to use and less susceptible to misconfiguration.
But neither Rack or Track Instruments are better or worse for performance reasons. For strictly performance purposes the important element is if you are using the VSTi for multi-timbral sounds or not - this is for both Rack & Track Instruments. For example having 8 instances of Kontakt each running 1 instrument is preferable to 1 instance of Kontakt running 8 instruments. This is because the multi-timbral instance will be confined to using one single core of your CPU. This increases your chances of overloading that single core. But when using 8 instances of Kontakt the same work can be spread across multiple cores - reducing the risk of glitches and dropouts. The other advantage is having each Track be a single Instrument is easier to use when mixing etc.
So in general (and with plenty of room for exceptions):
- Use Instrument over MIDI Tracks because they are simpler & easier to work with.
- Avoid multi-timbral VSTi use to reduce potential performance problems