Sorry to say this but I totally disagree. The question in the earlier Gens is not how few the Pokemon are obtainable, but rather, how are you going to obtain them. Gens 1 to 3 is the gen where it is almost impossible to complete the Pokedex unless you cheated or attend events to get Mew, Celebi and Jirachi(to name few). And as you said, the poor connectivity during these Gens that requires link cable made it almost impossible to complete the Pokedex.2. Pokédex is way easier to complete. While Wi-Fi is a definite upgrade over link cables, on the other hand, there were only 251 Pokémon max by the end of the 8-bit era. And, only two of those were event Legendaries, both of which could be obtained by exploiting glitches. Suffice to say, there's a reason why "Gotta catch 'em all!" was dropped after Generation 2.
As of now, I have the copies of every game in PC. FRLGRSE and X/Y are the only surviving cartridge that I have right now. Everytime I play every game is the opportunity to refresh every stories that we have enjoyed.
I think no one needs convincing. Because most of us loves earlier gens.Obviously, I can't convince everyone to like the earlier Gens, and nobody has to play them if they don't want to, but they still have their advantages.