Fleet owners and managers do these kinds of studies. There are publications that cater to fleet managers, google some and search around and you can find them.
I don’t do preemptive replacement of parts, with the exception of motors with timing belts. Otherwise I change oil, and other fluids, and fix or replace as needed. I don’t replace parts until they either break or produce symptoms due to wear, such as a noisy or clunky CV joint.
The two scenarios in the OP will need tires and brakes to be road worthy and safe. The 2nd (the latter) skips changes of other fluids and I’ll presume would not do a timing belt job on an interference engine either. What other parts would be “pre-emptively” replaced in the 2nd scenario? Lots of cars go 100K now on the original spark plugs. In scenario #1 I’d replace the plugs once and add in a few air filters. In scenario #2 you’d skip the plugs, but what about air and other filters. Doing maintenance as per mfg recommendations in scenario 1 would add about $1,000 to 1,500 the higher number for a timing belt engine.
If you want to just do oil changes and nothing else and trade every 125K miles that might work for you. I drove a company fleet car for many years and the replacement cycle was 3 years or 55K miles. Basically those cars needed oil changes, brakes, and tires. Some shops tried to sell me struts, and claimed torn CV boots, etc. We had to call the fleet dept. for any repair authorizations and most of these were bogus upsells that got rejected.
If I was driving a fleet car today (last one I had was an '00 Saab 9-3) I’d be comfortable running them up to about 100K miles. At the time the fleet dept turned them over at the 3yr 55K miles point because the values dropped off significantly if you got into 65K and more miles. It was residual value of the car that dropped off more significantly with the higher miles that determined when to trade, not increased costs of repairs. Taking a fleet driver off the road while sitting for repairs and rental costs were also part of the equation and these items increased significantly after 60K miles.
The issue for me is do you plan to keep your new car for 100K miles and then trade it in? Or, keep your new car for 10+ years and over that time rack up 200K+ miles. If you opt to trade in and drive 25K miles a year you’ll get a new car every 4 years and you can likely skimp on maintenance. Oil changes, tires, brakes, some filters and fix what breaks. If you opt for long term ownership of the same car; you do oil changes, tires, brakes, some filters, fluid changes (coolant, brake, transmission, differential(s), timing belts (if applicable to the motor), and fix what breaks. Not that much more money and you don’t have monthly car payments for 5 or more years before you get another car. At this time I have 3 cars and zero monthly car payments. My years of driving 35K miles annually are finished and so are my years of making car payments.