I was confused too, but I believe that it refers to the Pareto Frontier: the best set of solutions to a multi-objective problem.

Look it up, it’s a bit difficult to explain concisely in words but it is intuitive visually.

If we are thinking of intelligence and price, a model will be in the Pareto Frontier if there’s no cheaper model of the same or higher intelligence. Or if there’s no more intelligent model for that price or lower.

EDIT: See this chart from Artificial Analysis: https://artificialanalysis.ai/#intelligence-comparison-tabs

So for example DeepSeek V4 Pro can be considered a frontier model because there's no cheaper model that is as intelligent.

For any solution in the Pareto Frontier, there no "no-brainer" alternative, in the sense that there's no other option that is better in some way without giving up something else. It's the best of its "weight-class".