For one they don't give you any indication of the values you're trading, which is critical.
If you think about it, for 100 000 lot accounts, most people would put down $10 000 which is already a fair whack. And the minimum you can trade on that is for say EurUsd 0.01 x 100 000 x exchange rate. So even your smallest trade is already 10% + of your capital. That alone will make any portfolio fail. You have to be the best of the best to make that work.
So you need $100 000 at least to get started, or better trade sizes.
On platforms like Oanda the value of what you put down is reported and clearly shown. On MT it's not. Also the trade sizes on Oanda ensures a better rate of survivability, which is why they had a 50% client win ratio. Or should I say 'had' till they started raping peoples spreads. For example on O you can make a setting to use 1% of your leveraged capital and you'll always get the correct value trades, not to mention a reasonable risk. Something you can't even begin to do in MT unless you code it yourself and have $100 000 in your account.
There is the much rumored plugin, which means they can play with your feed. Put in spikes etc.
I asked a friend of mine who owns a MT brokerage if the stories are true. And he said and I quote '...the broker can make it very difficult for you...'
He wouldn't say anything else other than that, but the implication is clearly that the broker can do things with MT to make you fail if you don't fail yourself.
The average broker model is clearly an expectation of your failure. That's how they make their money and why if you're doing well your account gets frozen or they pick a fight not to pay, accuse you of arbitrage or something, google around and you'll find many examples of this behavior from brokers.
First thing I do when I look at a broker, is google to see if people complain about frozen accounts. If they do, it's bucket shop.
The ECN's are different. They do put your orders through to market. You can easy recognize them by being unable to send an order with a SL or TP. But the majority of them are full lot brokers, need $100 000 or more to stand any chance of making it.
MT5 is better, it does report position values. But the take up has been so low. And again full lots, I haven't found a micro lot MT5 account yet.