If you buy a mining contract and hold it, then it probably won't be profitable because you will end up with less bitcoins than the amount you put in. If that is your goal, then I agree it would be better to simply hodl the bitcoins themselves and your calculations seem to support this conclusion.

What you are forgetting is that you can profit by trading the mining contracts themselves.

Don't forget that you can sell your GHS after you are done with mining And the price of GHS haven't moved much the last month

forget cloud mining generally, and cex.io especially
we can't make profit from it
since bitcoin difficulty skyrocketing every 12 days, it will make our profit from cloud mining fewer every day
don't forget cex.io maintenance fee, it's too high
and their GHS price is overpriced!
stay away from it

What great bitcoin wisdom advice here....'Better play roulette' 'I advise you to play at a casino'

OP, if you buy any cloud mining contract and sit back and do nothing you are unlikely to come away happy. If you have the time to educate yourself a bit about what you are getting into then perhaps you can profit or at least learn something. With CEX and GHS you are buying a trade-able asset with a very liquid market, which also happens to generate dividends in the shape of mining returns once you have bought them.
GHS pricing has been downwards for months pretty much inverse to difficulty increasing, however that relationship has disconnected for the past 6 weeks or so as GHS pricing (in its market has found a bottom area and remained above that and slightly trending upwards).

thresher says CEX was the first one of 3 he pulled out of due to high costs on 'their shit scam site' but what he didn't tell you is that his PB money is completely gone as it can never be 'pulled out' and with Havelock the liquidity is so low good luck getting that out at a price you'd like.

Again educate yourself a bit about what it is you are buying into and the reasons for doing it and make sure you have an exit strategy as well as an entry.

CEX pricing has been like this since day 1.  It is well known that it is overpriced, at least for anybody who can do rudimentary math. Most people buying/selling on there end up trading in hopes of selling to somebody else for a higher price (greater fool concept).

If you're going to trade, you might as well trade on an exchange...

Well I believe that is their business model.  They were in effect selling the work that other miners did at a higher price than it was worth.  If you mined or are mining there, you are the power that they were/are selling.

How else could they afford to operate with 0% fee?

Well they will have their profits (which I'm not against) and somebody will be left with nearly worthless shares

I didn't say they were good, I said which one was the worst. Pb right now I believe I am 0.04 down at the moment (probably will pay off overall), I may have cashed out of havelock with profit, cex.io I ditched within the first two weeks, or less.  Spent roughly 0.1 btc at all of them (I go through gambling phases, and when I win, I blow the money on nonsense lol.) I haven't monitored them really because I honestly didn't give a shit.  All I know is pb and havelock seem legit, and cex.io is a scam.
I never saw pbmining or havelock produce a negative mining balance...... What I have seen is cex.io scamming people from day one, with a bunch of trolls that put referral links in their sigs to get money by scamming others into their bullshit. 
Why does one buy cex.io gh?  To dump on someone else for higher.  If that isn't the plan please let me know how your increasing your btc by mining there.

I'm not sure why you say it was worth it when you would have earned more if you didn't reinvest into their business model.

They charge a very high maintenance fee, the price of GH is dropping quite fast, the withdrawal fee is 0.001. You should have lost a portion of your money.