I switched all mine from 1.0 to 0.5 and added a few more routes with the extra hours available, and made +40k to my DOP. 1 airplane, 9 routes (no more than one 0.5 route to any one airport). They weren't even really great airports either.
Realistic? No.
Better profit within the current rules? Yup.
Last round, I only had 1 route where 1.0 had a bit more profit than 0.5, this time, 1.0 has always had more than 0.5, but not enough to make 1.0 more profitable than 0.5 overall. Why do 1.0 when I can do 0.5 on one gate and another 0.5 on another gate and make double+ the profit?
I do agree that the rules should change so that no plane can do more than one single 0.5 unlinked route. By "unlinked", I mean not doing a base->base->base->base run, which should be allowed, but I don't think the game actually factors that in at all?
Lets see what this one single airplane does.
1. Flies to airport #1 loaded with passengers - uses up hours.
2. Magically reappears at base - uses no hours to get back
3. Flies to airport #2 loaded with passengers - uses up hours.
4. Magically reappears at base - uses no hours to get back
5. Flies to airport #3 loaded with passengers - uses up hours.
6. Magically reappears at base - uses no hours to get back
7. Flies to airport #4 loaded with passengers - uses up hours.
8. Magically reappears at base - uses no hours to get back
9. Flies to airport #5 loaded with passengers - uses up hours.
10. Magically reappears at base - uses no hours to get back
So on & so forth...
Even though it's currently within the rules, it's only just slightly less "cheating" than having multiple 0.5s on the same route.