I don't see it that way.
The few anecdotal reports of PHEV usage report getting 2K+ miles on a tank of fuel.
Obviously engine maintenance would go off of engine hours, not mileage in this case. Manufacturers would likely have you change oil every few years based on hours.
I still don't see what the big deal about ICE maintenance is, it's practically nothing as is.
I also don’t see all the complaining about ICE maintenance. I have 3 ICEs and 1 EV at my house, all were purchased new so I’m the original owner (2018 tesla model 3, 2013 Lexus LX570, 2004 MB e320 4matic, 2015 Subaru Legacy)
I do all my own PM and most of the repairs. Have all the tools I need including a lift.
This year I’ve probably spent 6 hours on maintenance between oil changes, diff fluid, break fluid, and summer/winter tire swaps. I enjoy working on cars, I blame much of it on my first 2 vehicles being a 1979 Jeep wagoner and 1993 Range Rover.
Some thoughts comparing our 4 vehicles
tire swap takes the longest on our Model 3 and Subaru Legacy, they have the smallest most specific Jack points. So the EV takes more time here.
I do brake fluid exchanges every other fall when I do a tire swap on all the cars, I do 2/4 every time this fall I’ll do the Tesla and MB. So no advantage there, all about the same.
Diff/t case fluids, on the Lexus and Subaru I do every 30k miles, 50k on the MB. It is starting to concern me that Tesla claims lifetime for diffs, the diffs are pretty standard open diffs on the model 3, nothing special, connected to very high torque motors. Elon is a major BSer and like to claim no maintenance. I’m at 45k miles and 4 years, now out of warranty. I tend to keep cars a long time, I’m starting to think I should change the fluid regardless of what Tesla says. So I’m going to say a wash.
Coolant, did it at 100k on my MB, will probably do it at 100k on the Lexus. Again lifetime seems like a long time for the battery coolant considering they use G48, same as MB and BMW in their ICEs. I’ll probably say 100k miles. But no idea what the process is, in an ice I can do it in ~1hr. Let’s say a wash for now but could be longer.
Transmission. No transmission in most EVs. I do transmission fluid every 5 years in the Lexus, 7 in the Subaru and 10 years in the MB. Honestly transmission fluid is the easiest fluid, I don’t even put the LX on my lift for this one. EV wins here (will except for the Porsche that has a transmission)
Oil changes, on the 3 ICEs I probably do 4 a year. I can do all 3 in probably 1.5 hrs. EV wins here
Tires: so far my EVs have gone through tires 20-30% faster then my ICEs. So win for the ICEs.
My LX is by for the most PM heavy and I do fairly short intervals. But the vast majority of the time I drive it is off road it hard in very harsh conditions and towing a 7k lb camper.
So for people that own a vehicle less then 5-7 years it really it comes down to oil changes, which for most people is once a year. So for somone that has a car 7 years you are talking about the cost/time of 7 oil changes in an ICE vs one extra set of tires in an EV.