I agree. Some would argue that any bag that exceeds the sizer, even by half an inch, is the same as any other. I disagree. While some blindly follow rules, I'm about the end result. If a bag fits in lengthwise, taking up the "allotted" space, I don't care if it exceeds the sizer by a bit. It's those that take up more than their space (by a lot in the case you mention) that I object to.
Cheers.
I've seen passengers trying to cram in rolling duffels that have to go in sideways. If they can get them in, they take up the room of three rollaboards. Same with the 25 or 26 inch rollers. And all of these bags are too thick, don't want to go in the bins at all, must be squashed and crammed, take several minutes to get in there (during which boarding for the aircraft halts, as the doofus doing the cramming is blocking the aisle). I know that AA likes to man gates with only one gate agent, but I think they should require a FA to stand at the gate, pull these passengers out of line and check their bags. And charge them the bag fee. The FAs know which bags will probably fit and which ones obviously won't.