I've owned 1911's (not a Taurus PT1911) and I've owned a Beretta 92FS. I currently (for about a year) own a 1997 PT92, and I consider it the equal of the Beretta 92FS I owned.
The alloy frame is not a problem in any way. Can a careless owner scratch it? Sure. Just like any other alloy frame. I've seen well used military Beretta's with hardly any finish on the alloy frame still in service and still functional.
As for the locking block, Taurus 92's can break a block, just like a Beretta. In my research over at Taurus forum before buying my PT92, I found a few stories about broken blocks, but not many. In fact, there are a few guys there with older PT92's with thousands of rounds through them, still running the original block.
Since I didn't know the round count on my PT92 (even though it looked like new), I installed a latest gen Beretta locking block and pin kit, which dropped right into my Taurus.
1911's are great pistols...but I prefer an 18rd DA pistol anytime.