You may not like the education system, but in life you can't always just do what you like. Sounds a bit like you need to grow up a bit and learn what the real world is like.
The type of job you're talking about is often only done by some of the most experienced pilots, as it's single pilot low level stuff so a lot more risky than two pilots up high with autopilot where they are little more than systems operators. It's rare these days to get into single pilot vfr operations without some serious contacts, so you really need to start networking.
If you know the right people, school qualifications aren't particularly relevant, but if you don't have the contacts then good school grades could be the difference between being phoned for an interview or your cv going straight in the bin.
No reason not to do your best and get good grades. I hated school, still worked hard and got As and Bs, a good mental attitude to hard work can't be beaten in the real world.