Is the average car engine better at driving than the average light aircraft engine is at flying? I.E are cars generally more reliable at what they do.
I'm not trying to compare apples with pairs [sic] ... but I also know that there are similarities between the engines.
That is exactly what you are trying to do. The demands on the engines of aircraft and cars are very different, as has been said before - the average car engine is running at 15 - 25% power most the time, an aero engine is running at 60 - 80% most of the time, and sometimes at 100% power (e.g. on take off, go-rounds etc). They are having very different demands put on them, they are designed differently accordingly.
Apples and pears - how long would your Rover engine last if it was at 70% power most of the time with occasional bursts at 100%??
The overall reliability of both is high - i.e. within acceptable limits for most users for normal usage. Neither is "better" than the other because they are doing different things.
Which battery is "better" - those in flashlights or those in mobile phones?