But you are supposed to catch common pokemon, that's the quickest way to level up.

Assuming your goal is to level up. A lot of people were playing for the collection aspect.

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.

That's nice and all, but it's not fun.

It is fun when those common pokemon evolve into high CP Pokemon.

They don't though. Evolving gives you, in my experience, +100, perhaps +200 CP.

All my 10-50CP Pidgeys don't magically get useful by evolving. Though they do give nice XP.

Yes they do, my most powerful characters are all margikarp, psyduck, eevee, exeggcute evolutions. I have a 990 CP Pidgeot from pidgeys.

Power them up before evolving them.

Evolving doubles the XP usually.

I found plenty of rare Pokemon walking around while I was visiting London in late July, including a Dragonite.