Short answer: yes, a four city victory without conquering can be done (assuming you are playing on a difficulty level where you are competitive; if you struggle on Immortal you won't turn it around with a four city strategy). I won a four city India culture game ages ago on Emperor (which given the improvements to AI since then would correlate to King at best now). Size was Standard or Small; it wasn't my intent but 3 neighbors all forward settled me and I made due. I don't see any reason you couldn't win with a four city empire in current versions of the patch, but as others have said you would have to work with what advantages you can press: you're likely going Tradition-Artistry (strong capital will be a must), grabbing Wonders that grant percent yields (Mausoleum or Temple of Artemis, for example), settling defensively, making friends where you can, bribing for war where you can't. Your small empire will be hard pressed to influence runaways so you could lose to forces beyond your control but it should be doable. Are more cities better? Yes, of course. Why should a tiny empire that has fewer borders to defend, less resources necessary to expand, build, and protect, and fewer needs to overcome have an advantage over one that has spent the resources to expand? Bigger is going to be better if you can keep up your infrastructure but that's the challenge; it's easy to overextend yourself if you don't have a sound strategy. So while four is doable, 6-8 cities is more in line with what a small empire can limit itself to and remain competitive.