FWIW ... (what you paid for it
) ... I've been using MIM 3rd gen parts since I was introduced in them toward the end of the 90's, and typically found them to exhibit better, tighter tolerances than the same forged or cast steel parts.
Also, in my '05 vintage SW1911SC 5", the only part that "failed" after several years was a plunger tube (staking let go), which isn't a MIM part.
I'm a long time 1911 owner/shooter (and went through the Colt Model O Pistol armorer class), so I'm somewhat fussy about the quality of the parts that go in my 1911's.
Now, just like when we're talking machined forged & cast parts, where the quality of forged and cast may run the gamut of quality being anywhere from not-so-good to great, the same might be said of MIM. Also, in addition to the quality of the MIM material, there's the quality of the MIM molds to consider.
That's why we were told (in a late 90's armorer class) that S&W wisely decided to select and own the MIM molds used to make their parts, even when they're made by an out-sourced "MIM house" vendor, so they can have control over the quality of the molds, themselves.
I won't name the gun company involved, but some years ago I remember hearing how one gun company once took bids for MIM parts for their branded pistols, and when they got bids for the work, decided to use a vendor that offered a less expensive bid.