It is difficult to explain in short statements, but I'll try.

1. Bminer reports total hashrates for your GPUs. It includes all shares (accepted, rejected and the devfee). As a result, turning on / off devfee does not affect the numbers the disabled optimization on various places does affect the payout, which you might see less hashrate on the pool side.
2. The pool estimate the hashrate based on the number of accepted shares and the *difficulties* of the shares. Essentially hashrate = the number of accepted shares * difficulty. Pools control the number of RPCs sent to the pools by varying the difficulties. Therefore, it is quite normal to see that all miners report roughly the same number of the shares to the pool, but due to the differences in difficulties the payout could be very different.
3. Bminer right now does submit some invalid shares. My understanding is that there are benign and will not affect the payout. I got good results on nanopool / miningpoolhub, but at the same time I suspect that there are times that the pools are penalizing it. I'm looking into it in more details.
4. There is no points for miners developers (at least that's my view) to cheat / scam or whatsoever, as it is relatively straightforward to verify the payouts and to migrate between different miners. Cheating will not go far. My mission is to develop the most efficient miner available to help the users to get more hashrates from their GPUs.

Since the questions have come up from time to time I might spend some time to write out how the whole thing works. Stay tuned!