There's no doubt that MIR Pro makes traditional approaches to mixing look a bit antiquated 😉, and less individual signal-processing is needed for fast and convincing results. But while MIR Pro offeres a unique combination of possibilities all by itself, I think a well-sorted toolbox like Vienna Suite is always a good thing to have - especially when you plan to work with 3rd party libraries an/or raw audio data, too.
- Compressor, Limiter, Multi-Band Limiter ... I couldn't mix without them (especially not without the Compressor's "FAT"-mode 8-) ...)
- Analyzer, Goniometer ... we can't mix with our eys, but sometimes a quick "second opinion" is all that's needed
- Powerpan ... actually part of VE Pro (disguised as Channel Pan and as Matrix Mixer), but especially for Logic users a highly useful tool in any case.
- Exciter ... for some this plug-in alone was reason enough to get Vienna Suite.
- EQ, Master EQ ... well, MIR Pro comes with its own EQ plug-in which is a close relative to Vienna Suite's Master EQ, but my hand-crafted presets were made for Vienna Suite.
- Hybrid Reverb, Convolution Reverb ... although it's not so obvious at the first glance: A dedicated convolution plug-in can be necessary even when working with MIR Pro. Specialized IR-sets like Numerical Sound's SERT/FORTI collections rely on it.
.. I hope this makes your decision a bit easier.