I guess why build a big block or hemi when a 4cyl will get you from point a to b? like efi, serpentine kit are somewhat just for looks, but also for driveability. also did you see how big and heavy the old school alternators got when you went to 100 amps? plus they suck at charging at idle. with the modern stuff you get better low idle power, no dimming headlights, also you get lighter weight and more amps, also you get higher amps to run an electric fuel pump, dual electric fans, stereo system, efi, modern headlights so you don't crash at night or no one hits you cause they can't see you.
now we get the ac compressor, sanden vs rv2. giant cast iron 2 piston pump, very inefficient, hard time finding r12 these days, sanden is newer, parts are available, its lighter, 7 or 8 smaller pistons, less drag when running, meant to run with r134, etc.
power steering, on our kit we run the new zf power steering pump. this is the one that all the new hemi engines use as well as most other modern cars. these have options for remote reservoirs or pump mounted reservoirs. and they are smaller and lighter than the older units.
spring loaded tensioner, vs arm muscle for pulling up the alternator. belt stretch no problem, spring loading takes it up the slack, need to run dual old v belts, good luck finding a matched pair these days. belt springing when revving up or shifting gears or accessories coming on? no problem tensioner maintains a preloaded tension all the time.
again these kits aren't for everyone. did v belts work? sure but that was 1970 even new machines these days are designed to use poly v belts. the are quieter and rob less hp due to friction and they don't need to be over tightened to keep them from slipping.
every system has drawbacks, but if the modern oems weren't using them then there would be a better alternative. right now serpentine is a better alternative than v belt is it for everyone? nope.
