I had the same problem as you.
going from AMP MT5 demo to Rithmic Ninjatrader 8 demo and Quantconnect (backtest only) I always had high performance.
The problems with the future MT5 AMP SIM are:
1) the orders are executed at the last price for example my order to buy at the market price is executed at the bid level if at the moment the last price is the bid.
2) my order a market always started with a profit $ 0 (which is not fair).
3) I can instantly exit with a profit by executing a reverse order if the last price goes from bid (my entry for buy) to ask.
4) limit orders are instantly executed if the last price hits the level.
5) there is never any slippage for market orders. I went from $ 5,000 in demo to + $ 60,000 in one week. haha i wish it was true.
I added internally in my code a function which allows to calculate the exact profit but without much direction because the executions are always fast and there is no slippage.
So, I coded the strategy for ninjatrader and I shot it on a FIFO demo account, I went from 10,000 to + $ 40,000. It's crazy.
abnormally crazy.
although the executions are slower but it still remains illusory results.
To further verify, I coded the strategy for QuantConnect. the platform supposed to be the elite in the field of algorithmic trading open to the big minds of the world.
In 5 years of backtesting, I went from $ 45,000 to + $ 61,000,000.
the limit of madness.
But as a trader told me the best way to find out is by going live.