Yes, the common V-belt is still quite an efficient and long lived device, provided that the belt MAKER'S RECOMMENDATIONS are followed. Loads, speeds, number of grooves and pulley sizes are all specified, and when these are followed they are a quiet, long lasting power transmitter. Common mistakes I see are using pulleys too small, not enough grooves, misalignment and dirty environment.
Cast iron is THE pulley material of choice except for low power short run jobs. Unfortunately pulleys are sold in sizes much smaller than recommended minimum sizes for the various belt types.
Because you can buy a pulley does not mean it will be suitable. An A section belt needs a pulley of 4" or bigger. The B section needs 6" or more, and so on. Sure you will see smaller pulleys under your car hood, but an auto belt wii be a raw edge type, possibly with a cog pattern top or bottom, and is only a distant relative of the industrial belts you will buy in longer sizes for your generators .
So forget small auto pulleys . You will drive your car less than 1000 hours a year and the belts will be changed at the service interval. They probably absorb a couple of horsepower from your car, but your 6 or 8 hp generator can't afford it. So Google up your belt makers info and use it when designing a setup and you will not be disappointed.
Lister knew all this when they built the CS powered gennys in the 1930"s with 11 or 12" pulleys on the driven end, and they ran forever with maybe an annual adjustment, and only moderate tension. My VA SOM holds frequency and runs a full load with quite visible slack in the belts. No oil seems to get to the belts on this or my 8/1 when the crankcase breather is doing its job, as they do when correctly assembled. Modern automotive polyvee belts are popular on the grounds of slightly less power loss, but they sure need some extra tension on flat flywheels to prevent slippage.
Just the thoughts of a bush mechanic, Combustor.