ESD grounding and parallel resistance

The important thing is to keep the voltage difference between the person and the electronics to a minimum.  If both the PCB assembly and the person were at 10kV, there would be no damage to the board (or the person) when the board was touched.  By keeping the board on an electrically dissipative surface and providing a discharge path for the person (through a wrist grounding strap or a heel strap and a conductive floor mat) the voltage difference is minimized.   There are many more static-awareness concepts to discuss, but you may not have time for them.  Did this answer your question?

Not sure if you got your answers to this but there is some guidance in ANSI_ESD S1.1.
There is a little bit of validity to your colleagues concern.  You would have to set up your systems to accommodate for times when you have parallel resistance but there is so much range with the resistance suggested values, you should have much of a problem if you're using, I'll call it, typical electronics industry standard type grounding materials and equipment.  In our facility, our floors are usually around 1 X 10^8.  Our wrist strap systems are set at 35meg.  Any parallel resistance would still fall within recommended specs, as stated in ANSI document.  We do not require our employees to be wearing a wrist strap while standing on the grounded floors and while handling ESDS items.  However,  when they are gong to be in a seated position, they do have to be connected to our wrist strap grounding systems, because people are very likely to lift their feet off the floor, while in the seated position.  The thing to remember is, if they have the item in their hand while transitioning from a standing to a seated position, they should be placing the item on a grounded surface first.  If they don't, they are likely to be holding the ESDS item while they are just sitting down, potentially having broken contact with the grounding through the floor and just prior to plugging into the wrist strap system.  We train them to put the item down first, plug into the wrist strap system, sit down and then pick up the item to continue with what they were doing.