How do you know unless you have used all of those platforms and tested them out? Have you scalped with Etrade, Schwab or TDA and timed them? I don't day trade or scalp but my executions using one of them were all instantaneous as far as I could tell, without using a timing algorithm.
I don't scalp either but I do day trade, and I have had no problem with TDA for options. Lightspeed is a much better choice for stocks.
Have you looked into Tradenet? I don't know how much buying power $3000 will get you. But I know $9000 will get you buying power of $240,000. From what I understand, Tradenet trades CFDs, which U.S. citizens are prohibited from trading. However, with Tradenet, they get around this hurdle by allowing you to trade under their account as a "prop trader." Tradenet https://www.tradenet.com/ One Blogger's Experience with Tradenet: http://thetradingdentist.blogspot.com/2018/07/what-is-tradenet-funded-account.html
This guy is a scam. This is a bucket shop like Suretrader was. He takes your money, and gives you a demo account to trade which you think is real. Since most traders lose all of their capital quickly, no one is the wiser; and for the occasional profitable trader, he has the capital he confiscated from all the others to pay out the "winnings" of the very, very few. Thankfully he was enjoined from accepting any more US based traders and funds.
If the rules are clearly spelled out and transparent and they strictly follow without deviation, then you cannot say it is a scam. They operate like a casino rather than a brokerage. Casino allows you to bet on sports, horses even elections and this is similar, the bucket shops let players (traders) bet on stocks instead. Another thought: How is this different from us trading derivatives? We make side bets on the underlying through CBOE who manages the trades and guarantees the payouts?