yes, Horizons player CAN have advantage over guy owning only core game.
Is it fair? ... putting aside what I think about "fair word meaning" it imo fair is (yes, "fair" is very personal evaluation imo). FD never promised that ED core game owners will have the same "chances" how to play ED and that they will not get disadvantages when confronted with "next" season owner. Plus they need to have some way how to "financing" running game, its maintenance & further development ... and did decision how it will be done. It is for them to evaluate if that was good or bad decision. But when return back to compare Horizons vs Core game player, game offer different play mods which can be used (and it works) to avoid above mentioned direct confrontation.
Should be 2.1 part of core game? ... absolutely, imo ED should be released as it is now, 2.1 should be the core game (or maybe season 2 should be?). This is what I think about it (but this pov can be heavily influenced with my own experience), BUT such things obviously in RL are not so easy to solve/have planned/get running/get financed. ED have its own evolution with success and failures, some see it fair and have fun, some do not have fun and/or see it as unfair.