There are a lot of poor quality contractors and carpenters out there, when people sign up for having handrails system installed on a stairway. They are surprised as to what was built. A Lot of contractors build a knee-wall 2”-3” above the tread, covered by a wood trim board and then the handrail system on top the trim board, because they don’t know how to install a exposed tread system.
A cheap exposed tread system looks like this photo. What makes it look cheap is the skirt board. The reason is that it does not match the baseboard joining up with it.
If you have a smart carpenter use a 1”x 8” board and a piece of 5” tall base to make a custom make skirt board. Join them to together with a biscuit jointer and glue. Than run it through a surface planer and bring them down to the same thickness. A few minutes of light sanding, and your new skirt board is ready to be custom cut.