I think the game absolutely needs PVP / better gym mechanics and trading to survive. Right now the emphasis is 95% on collecting, which is why people are losing interest.

And it wasn't going fast enough for them?

But maybe they didn't want it to go fast. Maybe it was supposed to be unfeasible to get a full set in a reasonable amount of time. This doesn't seem too unlikely if they want to implement trading at some point.

True, "Gotta level up" is a far less compelling motto.

I don't think the motto is the 'foundation' for gameplay. Last I checked pokemon was also about battles.

Um yes, its called 'evolving' your pokemon. Commons evolve into new high CP pokemon which fill up your pokedex AND give you high XP in the process.

Yes, but there's only one evolution track per pokemon (except Eevee which has 3 in gen 1). The optimal strategy for grinding experience is to catch a million pidgeys and evolve them all into Pidgeottos for the experience and then transfer them because Pidgeot isn't that powerful of a pokemon. The optimal strategy for building the pokedex is to catch enough pidgeys to get a Pidgeot and then you don't need to catch any more pidgeys.