I think the balance is pretty good. Though most Colonist options are essentially valued by how fast they help you get Trade Routes going. Will be interesting to see if they do fix Trade Routes how that will affect things.
Artists have the edge for getting the first internal Trade Route in many cases because of a faster Colony Initiative.
Aristocrats often have the advantage on getting the third city because of the faster rush of the second Colonist.
Scientists can help research Pioneering faster (sometimes the limiting factor), get invincible Trade Units faster, and generally get to Spies and Autoplants fastest. So while a bit slower starting, they're still strong.
Engineers can sometimes get a faster start than Artists even towards the first internal Trade Route because of faster Explorers, Trade Depot and/or Trade Units builds. Faster Explorers especially have a very large volatility. An extra Culture pop can completely negate the Culture advantage towards Colony Initiative, a Solar Collector can mean a much faster 3rd Colonist rush, a Crashed Satellite can mean a lot of things, Affinity is huge, and a Signal is crazy OP.
Refugees are the hardest to quantify and use properly. Health turned out to not be as big a factor as it looked like, but early pop growth is silly fast. You need extra Workers ASAP to keep up with Refugees. As far as direct outputs they are effectively some form of hybrid of Scientists (Science from extra pop, extra Academy) and Engineers (extra Mine) and/or Aristocrats (extra Generator), and rarely Artists (Gold, Coral worked early). As well as any direct output increases from working more tiles.
Refugees also give the very strongest internal Trade Routes. You can easily lower food surplus down, but if you have Refugees a city's max food surplus is always 2 higher than otherwise. That leads to wider possible variation on the Food side and so more potential Food from Trade Routes.