Wrong, and wrong.
1. The FISA court is not a rubber stamp, and if it was, then what would be the point? A rubber stamp court wouldn't serve any purpose at all. You could just move the stamp to the wiretapper's desk and call it a day. Fact of the matter is, the FISA court is extremely strict, and will toss out anything that's not up to snuff.
2. The 'after the fact' warrant sounds fine, unless you take into consideration that the pre-application process can take weeks, or months. The process is long and grueling to ensure that any packet that makes it to the FISA court is going to get approved.
The reason that the court's approval rate for warrants is so high is because said screening process is very tough. Theoretically it sounds plausible, but in reality there's very rarely a way to just gin up a warrant in 72 hours.