One time the commercial AC broke, the splits were NOT able to carry the extra weight.
Thats simply a capacity issue.
Most "commercial" ac units aren't designed to run in the winter. If one does choose this route it is important to get a contractor that understands the need for cooling in the winter and not just install a freeze kit as an afterthought.
A great many computer server rooms are cooled by mini splits due to the inverter tech being particularly suited to running when the ambient air temperatures are cold. I have seen Mitsubishi minis that were speced to run as low as -27 outside. They aren't just on or off like most AC units are. The compressor and both evaporator and condenser fans can run just as fast as required to meet demand given the ambient temperature. If it's cold outside the condenser fan may not run at all and the compressor isn't working very hard. Installing a freeze kit on a standard AC unit is like a bandaid.
I would rather have multiple high quality minisplits in a large grow than one big commercial unit. Better energy efficiency. If you are worried about a unit failure just have one extra unit in the room. So if you need 12 tons, get 4 x 4 ton units. Have one in auto cool mode set at a temperature just a little higher than the room should ever get. The extra unit will just idle circulating air and wait for a cooling demand. If there is a failure the extra unit will start cooling to keep things from getting out of whack, you can then turn it down a few degrees and let it handle the load while the broken unit is repaired or replaced.
To have a second backup commercial unit of 12 tons would cost more than having a spare 4 tonner.