Well it doesn't as you'd have to station commanders 24/7 across 3 platforms
The proposal makes everyone fortify the same way- inbound. To mess up fortifying you only need to visit the capital. Most switched on powers know which systems are fortified as well as when.
and it doesn't solve the 5C and bot problem which have largely been responsible for the collapse of every Power at one point.
Open on its own indeed is only a mild anti 5C measure- it only works if you can actually get to see your suspect 5C commander. However, it does work. A number of times 5C activity has happened and having flown out had chats with the people doing it, only to find lost players to bring into the fold.
The most potent anti 5C measures are weighting, which will make weaponised expansions much harder to do.
The bots & 5C also probably have access to the functionality of the trainer that allows instant travel between systems so good luck shooting them down even in Open.
Thats on FD to sort out, not stop features because of cheats.
As long as turmoil is done by economics you'll never solve anything.
Open benefits everything- if powers wind up shrinking it means more turmoils, more systems up for grabs and more squabbles. You will get situations like several powers racing for prep in the same system, with players kicking the other players to slow them down- which is the point. Open only acts as a modifer to current patterns. If you can slow, deter or stop another power directly its giving you more tools to fight with, not less.