>>50956853Steel literally defines the type chart.
Fighting and Fire were completely ass typings in Gen 1 (a gen dominated by Normal types btw) and became nearly required coverage Gen 2 onward because Steel is that influential.
Ice went from the best offensive typing to above average because Steel (also technically Fire) resisted it in Gen 2.
Ghost and Dark went from good coverage to some of the best coverage options you can have in Gen 6 despite Fairies because Steel is that important.
Giving Haxorus part Steel typing more than makes up for the Ground/Fighting weakness by giving it a ton of resistances, immunities, and making types neutral. You also get STAB Iron Head for Fairies.
There really is not a single Pokemon that would be worse off with Steel, and that even includes Rock types.
