Verified answer

Some other good Steel types to consider are: Steelix, Metagross, Lucario, and Excadrill. If you aren't against using legendaries, Genesect, Diagla, and Jirachi are good choices too. I would recommend Skarmory, but Skarmory is better to use in a competitve battle setting, and not a regular in-game setting (which is what I assume you're doing). The other Steel types you've chosen are very good.

Skarmory, Steelix, Metagross, or Bastiodon. Personally I would switch Heatran, as I don't feel right using Legendaries.

Metagross would help out a lot, Excadrill id you are not doing double battles... (two of his best moves for him hit his team and are ground.. ) if you do not want to rick excadrill use a Lucario instead for hs massive damage output.

skarmory

ferathorn

lucario

dialga

metagross

steelix or metagross

steelix (onix evolution)