Can't speak for all regionals but I know mine doesn't just hire anyone who can check a box. We do care where they built their time at. The ones who built their time flying around VFR in the pattern for 1500 hours will still get a call, but they'll have to prove themselves in the interview and then in the simulator, just like every other applicant. Someone with a poor background or excessive checkride failures isn't going to get the call. Our classes haven't always been full for that reason. The company isn't going to invest thousands of dollars in an applicant if they don't believe they can succeed.
CFIs who spent over 1200 hours keeping themselves and their students in controlled phases of flight and out of dangerous situations have a lot more experience than the 250 hour commercial pilots of the past. After spending hundreds of hours teaching students maneuvers in a single piston at low altitudes, and how to land, you simply have a better handle on flying the plane. Mistakes are made and you learn from them. There were quite a few instructors I knew who were weeded out either by realizing it wasn't for them, by the company employing them, or with a few blemishes winding up on their record. 1500 hours is a long time and takes reasonably at least a year and a half to accomplish. A lot can happen and a lot is learned during that time period. We never stop learning but those first hundreds of hours gaining a high level of respect for how an airplane behaves in different flight regimes produces a better pilot. As a CFI building hours, you are as much of a student of the profession as the one you are teaching, just at a higher level.
Of course there will always be a few who slip through the cracks or where the system fails them, that's true of any industry. I think the 1500 hour rule has made commercial aviation incredibly safer than it already was, particularly at the regional level. And the results speak for themselves.