OK. My two cents worth.
1. The 121 certification process is very hard. It's a huge barrier to entry for would be airlines. If it wasn't, it wouldn't be worth nearly as much (which is good for shareholders).
2. Very few airlines start out with wide-body aircraft. Most use a later model narrow body aircraft with fewer exits meaning that the mini evac demo is usually almost a non-event in the initial certification.
3. After certification, when adding a wide-body aircraft, the airline has to do a mini-evac for that aircraft but there are a LOT fewer eyes on the demo so, in reality, it gets a little less scrutiny. Usually just the local folks.
4. The FAA follows their certification guidance very closely. They don't let the applicant airline interpret the rules and guidance.
5. There are lots of slide problems out in the industry. Most are attributed to sloppy maintenance or careless operation.
6. You can't pass off the blame for slide failures to the outsourced maintenance organization as much as everyone would love to. It just doesn't make any difference to the FAA. The slides work or they don't. It really is just that simple.
All IMHO