I just tried again - Indeed the scrollarrows do appear when "All tabs have same width" is enabled, but the size of each tab has to be extremely small (like 3 characters or one icon (if enabled) before you see them.But now they appear. Independently of the setting.
Maybe it would be an Idea with a setting for the minimum title length, just like there already i a setting for the maximum title length.
But nonetheless - mouse scrolling still doesn't seem to work if "All tabs have same width" is enabled