yup. And last time i checked Normal/Steel & Rock/Steel were bad combos.
That's why he said
pretty much. Steel goes great with nearly any type although there are some types Steel goes with that compound an existing weakness which can hurt.
Heatran for example loses its Fire weakness thanks to its secondary Fire typing (in fact it becomes immune to Fire thanks to Flash Fire unless the Attacker has Mold Breaker or an ability like it like TurboBlaze) but doubles its Ground weakness and Aggron whose Rock typing neutralizes its Fire weakness but doubles its Ground and Fighting weaknesses. On the upside, both gain a good offensive STAB on Fire and Rock respectively. Heatran despite a 4x Ground weakness is still great since it still has a ton of resistances and good bulk all round. It's Speed while not great isn't bad either and it can boost it now with Flame Charge. Aggron does still have a fair few resistances and great Defense but its 4x Fighting and Ground weaknesses as well as its poor Special Defense really hurts it Defensively. Offensively, Aggron's Speed hurts it although not much can take Head Smash without resisting it and having good Defense to back it up and it can still boost its Speed but even after a boost, it's still not super fast.
Steel Types aside, Water / Electric and Water / Ghost are pretty cool typing combinations. Both have a unique set of resistances and both have a good STAB combination too. Rotom-W (with Water / Electric typing) even has Levitate to cancel out its Ground weakness (Mold Breaker is still a problem although the only commonly used Pokemon that has it is Haxorus).