The forked currencies are just the same as altcoins, you can't sell 1 Bitcoin Cash for $7000. The fact that people are willing to accept money for them doesn't change the value of one Bitcoin.
Each of these other "versions" of bitcoin were created by a fork. As far as I know, when a fork happens you get an equal number of "new coin" as you have original coin. Seemingly creating value out of nothing.
If you put a sell order at 7,000 with a volume of 100, it would (likely) cause a flash crash
You can see flash crashes all the time when someone offloads a bunch of coins without balancing across exchanges.
Plus, you would have to find quite a few people that wanted to buy coins @ 7,000 and finding them before your order causes a flashcrash isn't likely.
Both sides of the SegWit fork (SegWit1X vs. 2X) ~Nov. 16) are intentionally crippling transaction speeds/costs to move transactions off the blockchain and into the pockets of said corporate interests.
The true spirit and potential of Bitcoin lives on through Bitcoin Cash.