I agree with your write up above(about delaying the orders). The reason broker may hold your order is because they have to pay the exchange proportionally to amount of traffic used. So if client sends limit order far away from the market and then cancels it, that is a waste of resources that can be avoided most of the time without adversely impacting the client. Also, it’s possible that the broker did send the order to exchange and it did provide liquidity but due to some bug it was not accredited correctly(the liquidity flags are a mess)
As far as IB, they provide lots of value add and are not really catering to DMA client. After fruitless discussions I just decided that the benefits overweight the restrictions for my trading at current time.
Keep in mind that brokers are middlemen and the margins are thin, so I wouldn’t say their intention is to screw the client.