The only issue I can see from this is that you might not have gotten a high enough temperature for "scharf anbraten" (searing?) the steak. And it certainly looks like you're missing some nice Röstaromen. Having a heavier pan and a hot stove helps with that, but cast iron isn't necessary in my opinion. I have a nice steel pan and it works.
Choice of meat is probably an important factor, like you describe, but I'll need to experiment more with that myself.