It's a mixed bag. On the one hand, we really do get a lot more liquidity thanks to having tons of fast market makers. You can get subsecond fills on most market

It's a mixed bag. On the one hand, we really do get a lot more liquidity thanks to having tons of fast market makers. You can get subsecond fills on most marketable or close-to-marketable (eg; limit orders within the spread) on most common stock listed on the NYSE/NASDAQ. But it's often not "real" liquidity. Let's say there's 100 shares available at $100.00, 200 at $100.50, etc. Such that there's a total of 5k shares on the book at this time at any price. But we want to buy 10k shares. The average fill price assuming no intervention and only marketable orders would be (100$100 + 200$100.50 + ...)/5000. An intervening HFT firm will only be adding useful liquidity if the average fill price drops somehow. Shittier algos will lose some money by lowering the average fill price so they match your order and get the liquidity rebate from the exchange. This adds true liquidity. But intelligent market makers generally will just add identical liquidity to what's already available but at 1 or 2 cents higher (and a few slots higher on the order book). As a result, you just end up paying more for the same quantity of shares. That's not true liquidity because it's really only triggered by your order, doesn't move the price significantly, and is limited to exactly the size of your order.