Your reasoning doesn't make a lot of sense... I'm 99% positive that not a single person at Game Freak has considered the battery life when designing the graphics. If they did, they probably would have advertised it more than enough. It's a nice benefit, but do you really believe that they would have put in fancy graphics if the Switch had a better battery life? And like Lonely_Dolphin said, if they really wanted to keep presenting Pokémon as a handheld franchise, they would've kept the handheld price.

I don't care much about graphics, but this fits in the general picture of Game Freak / Nintendo not wanting to invest in the games. Aside from the graphics, half of the Pokémon are still missing, there are very few innovations, it's one of the few games that still don't have a Dutch translation... There are plenty games that barely sell 1/10 of what Pokémon does, and that feel a lot more polished in every way.

Game Freak seems to realise that the quality of their games has little to no impact on its sales. They could probably cut their budget in half, and they would still sell 15 million. And that's a shame, because the quality of the franchise will only keep going down this way.