honestly, no i can't. It was just intuitive, so i won't even back it up. But i'll say that i was thinking about how team preview wasn't available until gen5, and i thought we should let the player have a feel of that, but this arguement is unviable as our region is gen6 oriented.
I don't think it wise to introduce an Abra here, because it leads to other things which aren't that important atm. First of all, we'll, as you said, need Hidden Power to be present, which leads to that we it to be of our choice, which requires us to mess about with IVs, which needs an IV Guru or something. So, doing all this just because we want an Abra available doesn't sound convenient.
Also, we don't need Abra atm. We haven't come much far from Golurkmoar, i don't think travelling back from the 4th town should be an issue as well, so i say we introduce Kadabra after the 4th town.
What we can do is let Abra be in the Pokemon Centres, but not available in the wild just now. It'll teleport us back if we want to, so that's that solved.
As for Fly, i think we should let it be, as it has nice power, no recoil, and it's mechanic is interesting as well which'll give the player an opportunity to experiment, and also fly somewhere else when he/she's nowhere near a PC
ps:someone pls explain me the logic behind the protagonists' names