Should be more like 70 and 140 on an old v2 like Port Hope, but generally speaking this sounds like normal behaviour.I assume that you are right, but that wouldn't have mattered in my situation yesterday. I was at Port Hope a few hours later and it mattered there as I was getting about 50kW, then the car beside me left and I got 100kW for a minute or two until another car pulled in.
Kemptville is a v3 so it is 4 stalls per cabinet and the newer cars max out at 250kW. My 2018 Model S maxes out in the 150-160 range on those. For the most part, sharing doesn't matter on a v3, but theoretically if multiple vehicles plug in simultaneously at a low SOC and try to draw 250kW each, they will be limited to some lower amount because each cabinet usually has a limit that is less than 1mW. That scenario is quite rare however, so I've only noticed lower charging rates on a couple occasions and it hasn't been that much lower.