Getting From Milan to Cannes

You can drive it but is it faster to do that? Travelers here complain about the cost of renting a car in one country and then the fee associated with dropping it off in another

The Thello train from Milan is your best bet, on most dates there's an afternoon train to Marseille that stops in Cannes, otherwise it's a quick change in Nice.
But don't drop the car at Malpensa : drop it at Milano Centrale if possible - you do have to drive in Milan a bit, but you'll be far from any traffic-restricted area (ZTL), and it shouldn't be too much of a hassle if you get precise return instructions and avoid rush hour.
If that sounds too difficult, you can also see if you can drop the car in Como Town. Then you take a frequent train from Como S Giovanni to Milano Centrale, and change to Nice or Cannes. It saves you the time to drive back to the airport.

Look at it the other way around. Where are you going after Cannes? Where are you flying out from?
If you are flying out from Milan (or anywhere else in Italy), you don't have the issue of dropping off the car in a different country, you can drive to Cannes and back.

Otherwise, as the others say, don't drop the car at Milan airport, as that wastes time getting into Milan city centre (Milano Centrale station). Drop it in central Milan, or Como town where you can get a train to Milano Centrale.

You can look up driving times and routes on the viaMichelin website: https://www.viamichelin.com/
That gives distances, times and costs (fuel+tolls). The times assume you stop for nothing, so add 50% pad. For Bellagio to Cannes that says:

Time: 05h12 (04h05 on motorways)
Distance: 435 km (393 km on motorways)
Costs: €78.96 (Toll €36.50 + Consumption €42.46)