Recent versions of git can align fields directly in the format string see How to align columns in git to improve formatting?

[alias]
        br = branch --sort=committerdate -vv --format='%(color:red)%(objectname:short)%(color:reset) %(HEAD) %(align:30)%(color:yellow)%(refname:short)%(color:reset)%(end) %(align:28)%(color:green)%(committerdate:relative)%(color:reset)%(end) %(align:25)%(color:magenta)%(authorname)%(color:reset)%(end) %(color:blue)%(contents:subject)%(color:reset)'