Careful? Where's the fun in that?
I hope you know just having a fighting move replace Iron Tail would screw Pikachu against Golett...It's just like if Ash were to battle Luke's Ghost/Ground Pokemon, Iron tail would be the only effective move, and it would be resistant, that's even a worse match up, but unless Pikachu stops learning NEW electric moves, and actually gives Pikachu something that can hurt ghost/ground Pokemon, and replace iron tail with a fighting move (since fighting covers what steel is super effective and more) then Pikachu really is screwed against certain Pokemon types.
Now, I always though that if Pikachu wanted to take care of Ground, Rock and Steel Pokemon at the same time, he should learn Grass Knot and Brick Break, replacing Iron Tail and Quick Attack, giving him more options in battle and a well versatile move set. Will this happen, nope. Why, because the writers love making Pikachu the underdog and even with a severe type disadvantaged, make it win and come out on top like a champion