Regarding interfleet balance.
Balance between fleets is a very difficult endeavor. So long as overall they are close this is unimportant. Ships such as the styx can only be 'loosely' compared to the Mars as each fleet has access to several different fleets. It is much better to balance within fleets, to ensure that no ship is obviously a poor choice compared to others in the list.
Regarding fleet lists.
I know someone brought this up, that IN/chaos don't make sense to have individual fleet lists. This is comparable to Space marines in 40k, who have several rule books for just space marines.
The reason why IN/Chaos fleets don't simply have access to everything like other races fleets, such as Eldar or Necrons is simply because they have FAR more ships, and in the interest of fairness these vessels are limited to accomidate races with smaller numbers of vessels.
If say Necrons had another 10 ships then there would be individual fleet lists for them as well.
Additionally, this is a way to provide character and to make players who use the 2 most-commonly played factions from looking too much alike. Think about it in 40k, what if every marine player just played with the generic codex, then things would be much more boring.
Regarding power of veto:
Horizon has power of veto on anything regarding Eldar. In fact, he is the only one with veto, as the eldar rules are his idea.'
Styx:
These quandaries are a little late in the game gentlemen. The Styx works for 260 points. I do not want to dig up old arguments. They are a substantial waste of time, and every person has an idea of what ships are useful and which ones aren't.
I believe the styx to be good at 260, Horizon does as well and Admiral D too. Not every vessel has to be in everyone's taste.