In the last versions of metronic the btn-sm is huge, I think you should revert it to the old size.

It can be done in _variables.custom.css adding this:
$input-btn-padding-y: .75rem !default;
$input-btn-padding-y-sm: .55rem !default;
$input-btn-padding-x-sm: .75rem !default;

But I think this is a more adequate size than the one used currently. The btn-sm is large that most default btn size on other templates.