Yeah, they are using double or triple the amount of chips for the endurance, since in an Enterprise product they can charge for it. And then they can also integrate en 8 channel (or more) controller, thus keeping speeds up.
Regarding the TBW to be lower on high performance drives, I believe this is artificially done so that users don’t write through their TBW values in the warranty period. If you give a drive 3600TBW but it can only do 500MB/sec, unlikely the customer is going to hit that in 5 years. If a drive can do 2000MB/sec well then they might so let’s give them a lower number to start with. 
Currently my numbers are still holding strong and both the 600TBW are still telling me they’ll do at lest 2000TB actually written, so we’ll see! 