I don't like this argument for three reasons:

1. The single thread performance gap is very small (5-10% depending on application) or even non-existent in some cases.

2. Your computer runs more than one process at any given moment. The more cores, the more processes you can run without an impact on performance

3. That single core performance comes at the cost of efficiency and general power usage. Intel has had to clock their 14nm process very high to achieve that small lead in single thread performance.