Solid vs stranded wire: not the bottleneck.

It doesn’t matter for high-draw tools. The resistance difference between solid and stranded copper wire of the same gauge is negligible at 60 Hz AC.

What actually kills performance is using too-long or too-thin extensions. A 50-foot 14-gauge cord will drop noticeable voltage under a 15-amp load, whether the wire is solid or stranded. Stranded wire is more flexible and resists breaking from repeated coiling — that’s the real reason extension cords use it. Solid wire would crack after a few wraps.

Worry about length and gauge, not strand count.