Whew !!! Well Hans, I'm gonna go out on a limb here and say that 'YES', they do the same job, albeit maybe not quite as efficiently. When all is said and done what the gun (steel or plastic) does is hold temporarily some number of cartridges and at some point fires some number of projectiles. I mean as far as most folks know. Now with tongue in cheek I'll continue:
You and I are both smarter than that so we understand all about how the extra weight of steel helps tame recoil better than plastic does, but generally speaking no/very few first time (or even relatively new) buyers will consider that even if he/she is aware of it ..... and figuratively speaking NO sales rep will ever offer that info to those first time (or even relatively new) buyers, so in the end 'YES' they do the same job.
And I'm pretty sure I'm not too far off when I say that one day steel will be a long, forgotten and/or unimportant material that guns were ever made from. Maybe not in your or my time, but in some time for sure.