This makes zero sense. It must be some other issue causing the slowdown (maybe an almost-full drive with no TRIM or hidden swap memory?). Fragmentation should not affect SSDs, since there's no read head to physically move to different locations to access data. Every piece of data on an SSD should take the same amount of time to access.
You're replying to a seven-month-old post. The issue mentioned in it is out of date, but was at the time very real.
It wasn't due to either fragmentation or reduced performance once blocks had been written, though; the issue was actually with JMicron controller chips optimized for sequential read and write performance, to create big shiny advertising numbers. These controllers were appallingly bad at handling random writes, and whenever the computer hit the disk with random writes (i.e., almost every time you did anything), everything would freeze for a few seconds. The issue is detailed in full here
, but modern drives using the newer Indilinx controllers no longer suffer from these problems. Neither do Intel X25 drives, though they cost considerably more than Indilinx ones.