If you can't evolve Eevee, it's value is drastically reduced. While it's a Normal Type and has value against Ghost Pokemon(and Psychic thanks to Bite), Pikachu has extremely high value in the early game due to the early route flying types and the fact it counters Misty(while having a decent shot against Brock due to Double Team). It all comes down to whether you want to be Gary, May or Ilima with your own Eevee or Ash/Ritchie with your own Pikachu. It's definitely Kanto pandering but in terms of games dedicated to Kanto, it's been a long time.
Couple questions I have is the flexibility of transferring in Pokemon from older platforms(aka 3DS/2DS or other handheld devices. Heck being Gen 1 Kanto, I'd be shocked if they allowed RBY Pokemon) and breeding. I mean if you got a Female Eevee starter... could breed an Eevee line for the game if you could evolve them outside and transfer them in for use.