Are the ‘cons’ of an argument counted as evaluation?

It depends on the question - evaluation could look at costs, depending factors, limitations, unintended consequences or short-long term effects.

The Ofqual Subject Level Guidance for GCE Economics defines evaluation as a balanced judgement supported by relevant material, which makes salient points, acknowledges qualifying factors and understands the limitations of material. (Where relevant, the judgement may involve developing and proposing solutions.)

The command word 'evaluate' will always require students to make a judgement or come to a conclusion by weighing up competing arguments or alternative explanations or policies and showing an awareness of the strengths of both sides of the argument and what other factors might need to be considered. To be awarded ‘strong evaluation’ judgements should be substantiated, i.e. supported by previous comments that have made use of sound and relevant economics. Real world examples are often useful to illustrate points and to add to theoretical evidence. Whether they would be essential or not would depend on the specific question.

Good places to look for further guidance are the mark schemes, examiner reports and exemplar material. These can be located on Teach Cambridge.