So update I found the company that lets you mark cells. So it is a feature, but I don't think it should be exclusively locked behind one company. It's too much of a nice QoL to only have in 1 of 6 playstlyes.
Also the method you use is a bit awkward - just bumping into cells to mark them. It would be nice to be able to hover over a cell and press/hold a button for marking. One last small thing is that the current marking mask can somewhat blur the lines between cells. It'd be nice if there was a marking method that kept the borders more distinct? But that isn't nearly as much of an issue. All you have to do if you're unsure is unmark one of your cells real quick.
Lastly, upon a complete playthrough, the virus molecules could definitely use some more spice. The Gray, White, Red, and Pink variants in particular are very simple to defeat unless they're hybridized with another type. Perhaps having a cluster of three or more of the same color will grant a molecule new abilities within its own variant.
Also the type rarity is a bit strange too. Calcium and Phosphorus are Rare despite being pretty harmless while Helium is Uncommon and Nitrogen and Oxygen are Common. Of course I imagine that may be moreso for variety than challenge, in which case fair enough.