Just thought I'd pop in to say that I have never used Steam, and I never would.
I am a subscribing player of AoC with only one account. It would seem I'm the 'odd one out' from reading this thread about people using Steam, running bots and not subscribing.
I play on Crom and the population feels healthy to me. I've leveled two characters up to 80 so far over the last few months and have always had people to adventure with in every area as I level up, the chat channels are always active, and I have had no trouble finding groups to run with when I wanted. It may be the time that I play due to my work hours ( US eastern standard time, I usually game from 12 noon to about 7pm ) but I've had no issues with population.