Their hardware is about 30% of their pool size let's say 20 Peta hash max or about 16% of the total hashing power of 120 Peta hash. Oh look it is already at your requested reasonable percentage level.
If only that were true that would be great. It appears they are attempting to obscure their hashrate by solo mining with some of it. Also many of their independent miners are using their cloud mining services which said miners have no control over that hashrate.
Your right in that I haven't really researched how much hash rate is really theirs on their hardware on the network. But I have no idea how to realistically or accurately do that. I, like most people, go by the pie chart on blockchain.info.
The Bitcoin protocol has a weakness with the 51% issue, having the market players discuss it as an industry is the way to find a long term solution.
It's not a weakness! Its the nature of Bitcoin. That is the way hashing entities "vote" to make changes.
Right now ghashio is approaching the power to "vote" with no input from others. That makes allot of people nervous since they think any fork they do will be bad for everyone else, maybe it will maybe it won't, maybe ghasio will never attempt to create a hard fork.