What is this pioneer spam people whine about? (v0.95 to 0.952)
1. The land is in shambles and 99% of it is ineligible for colonization. The limit on my city building is that I can't find a valid spot to build not the time it takes to spam pioneers.
2. Population only gives gold, production and research comes from buildings. Spamming pioneers means I don't have buildings means I am hopelessly behind. (building a careful balance of a few pioneers and many buildings though...)
3. Building up 1 or a few cities makes you better positioned to conquer the AI's cities (the AI spam pioneers so he is WAY behind on the tech tree and lacks the resources to mount a proper defense of their juicy under-defended cities)
... pioneers must first be used to build outposts which expand zone of control which expands (slowly over many turns) the "restored" lands in which a city can be built.