Just make a bind then you can click a button and place one.
I think the current system of markers is fine, it's less confusing with only two markers at once, and I haven't really seen a ton of issues regarding markers. Also needing one of the side menus to place a marker could get annoying, if any other one comes up like a map vote it'll get rid of it and you can't really switch weapons when its open. In my opinion it's more streamlined how it is now and less hassle placing them.