Two Gengars are harder than everything Poison-type you could throw at the player in RBY, plus Koga was that gen's Poison specialist.
Gengar may be a strong Pokémon, but fighting them over and over again is simply
boring and doesn't reflect all that well on Agatha as a trainer, to be honest.
While she didn't have a great selection of Pokémon to work with, they could've done better than give her an awful-mono-Poison team. Ninetales has always been able to learn Ghost moves, and it's based on a
legend associated with ghosts and witches, so why couldn't she have had one? And, in the games, themselves, Marowak is closely associated with the dead, and it's pre-evo can even be found in Pokémon Tower, so why not also give her one of those? I'd also throw in a Hypno, as it's a hypnotizer (an ability associated with ghosts back then) and is kind of creepy, in general. Now, her team would be Ninetales/Golbat/Marowak/Hypno/Gengar, which still keeps the "Ghost" theme and isn't nearly as boring or painfully easy to fight.
Of course, in GSC you have dupes, but GSC has more specialists than types, and no Ground-type specialist.
Yeah, that was sadly unavoidable, especially since they refused to give us a Ground E4 for whatever reason. Plus, GSC's E4 was one of the worst ever. Will was a horrid excuse for a Psychic trainer and E4 member in general, Bruno was as pointless and weak as ever, and Lance, bless him, was just a Poor Predictable Rock (a
Kadabra with Ice/Thunderpunch could nuke him). Only Koga and Karen were any decent and even they had flaws (such as using weak, underpowered Pokémon like Ariados and Murkrow).
In general the games without two regions don't have dupes
But, at the cost of having more limited postgames.
When playing XY/ORAS for the first time, being able to use an EXP share that will apply to all members rather than just the first was a massive improvement. For the first time playing a Pokemon game I was able to built an entirely balanced team and actually properly get to know lots of different Pokemon. In that respect, I think that ORAS (and by extension XY) have done a great deal to improve the enjoyment of the game for those players who either don't have a huge amount of time or (like me) find it a monotonous task and would rather just be able to switch between different pokes. I loaded my original Ruby game the other day and attempted Norman's gym, couldn't beat him with my Combusken and that was my only real choice to use - frustrating.
Well, that's a big reason why remakes exist in the first place, to fix the flaws of the originals. ORAS did a decent enough job of that, although they could've stood to include more Emerald features (such as the stronger Gym Leader teams and Gym Leader rematches).
I do agree that occasionally Game Freak can make things a little odd, like has been mentioned the E4 was almost exactly the same in terms of typings and that kinda thing. Which I agree was a bit odd considering the Pokes available within game, and it seemed to be overlooked when you actually stop and think about it.
As I said, the Hoenn E4 just wasn't thought out well at all. I guess since they were the first non-Indigo E4, it's not too surprising, but they could've been better. Of all the types that were available, why use ones that had already been used by E4 members in RBY/GSC? Especially, when said type had next-to-no representation in Hoenn? (*cough*Glacia*cough*)
I don't miss the Battle Frontier in all honesty, I still replay Emerald and I still don't get very far within the Frontier - it doesn't interest me hugely.
I find it to be overrated, myself. The AI cheats, it's hard to beat without "good" (read. bred and EV-d) Pokémon, and it (along with the other battle facilities) just doesn't offer much at all for people who aren't into competitive battling. I would've much rather gotten some actual exploration areas instead of XY's battle facility, though.