You have an assertion - that good employees who work together as a team outperform great employees who don't.
For a very long time I've been looking for a reference that provides some/any evidence for this, apart from anecdote or assertion.
Do you know any sources that show teams are more productive and creative?
I've read a heap of Jerry Weinberg's & friends work - this is one of their major planks. I believe it to be true, from my own experience, both negative and positive, I know it to be true, but haven't been able to find any hard/definitive evidence.
Calling It a Team Doesn't Make It a Team
First of all, the initial assertion is wrong. Sometimes it's true, but sometimes you can put a bunch of good employees together, call them a team, and find that they perform worse than the individuals would have done alone. It's like the little girl with the curl on her forehead. When a team is good, it can be very, very good; but when it is bad, it can be horrid.
Lincoln used to ask a riddle: "If you call a tail a leg, how many legs does a dog have?" Answer: Four, because calling it a leg doesn't make it a leg. And calling a bunch of employees a "team" doesn't make them a team. It takes time, teaming talent, and work to make a team.
Apart From Anecdote or Assertion
Second, consider the request: "apart from anecdote or assertion." You're not going to find any experimental evidence on "great teams" because it takes time for great teams to form. Thus, you cannot assemble some teams of college freshmen and expect them to become great teams in a few hours or days.
Nevertheless, I have done experiments in my classes (with computer professionals, not college students) that show numerically on some relatively small problems that team results can range from ten times better to ten times worse than the individuals on that same team. Since I'm telling you that, but not publishing in some psychological journal, this qualifies as an assertion. If you believe me when I tell you that I've repeated these experiments dozens of times, then it qualifies as an experiment.
As an experiment, it's limited by the time scale, as my Problem Solving Leadership (PSL) classes run for only a week of intensive team building. Most of the teams become very, very good during that time, but they don't become great. That takes longer.
Some Great Teams
In my consulting, I have seen many great teams over half a century. I remember them, because great teams are always memorable. But many people do not observe these great teams in their own organizations, largely because great teams in large bureaucracies know they have to hide from their own management. Why? For one reason, managers want to improve the whole organization, not just one team. That's admirable, but fails when it's connected with the fallacy that you can break up a team, put its members--one each--on other teams, and then the other teams will also become great. You build great teams one team at a time.
For another reason, managers worry that they will be judged by the standard of the great team. If all their teams don't live up to this standard (and they can't), then the manager's manager may think that the manger is not doing a good job with those other teams.
And, some managers simply don't believe it's possible for a team of software builders to produce software on time, within budget, that works well and pleases their customers. They literally can't see it when it happens, even when it happens consistently. One reason, of course, is that the customers of such a great team don't want the manager to see it, because then they may lose the team to the manager's attempts to spread the greatness.
Anecdotes from Sports
By the way, one of the reasons I became interested in teams early in my life was from observing what I call the All-Star Effect. Years ago, many of the professional sports held All-Star games in which the championship team played against a "team" composed of the star players from all the other teams in the league. Over time, though, people began to notice that the real team always won over the pseudo-team--a bunch of outstanding players thrown together for a short time and told to become a team. One by one, the different sports stopped this practice and converted to an All-Star game that pitted stars from one half of the league against stars from the other half. This new format was very entertaining, but told us nothing about "great teams."
More recently, the American basketball coaches learned this lesson about international play. For many years, the American stars were just so much better than the players from other countries that the Americans could throw together a bunch of them, call them a team, and have them dominate every single competition. But as the standard of play in other countries grew, the American All-Stars began to lose. Now, when the Americans put together a "team," they insist that the players work together for much longer periods of time before taking the court for official games. And now they are doing much, much better. Talent helps, of course, but talent plus talent does not automatically make a team.
What Kind of Team?
Finally, in different activities, the meaning of "team" changes. At one of my clients, the manager kept insisting that his employees work "as a team." Since they "team" consisted of field support agents who worked individually in different parts of the country, nobody knew what he meant. Finally, someone worked up the courage to ask, "What kind of team do you mean?"
He said, "Like a ski team!"