It kinda depends. I definitely can read way faster than usual if I try to. I'm pretty sure it's because our brains have seen so many words they have an autocomplete grown in. Focus is hard to tell because the sample is so short, but I feel like it might have more to do with reading more information in the same amount of time it takes us to get distracted, rather than actually improving the capability to focus.
Also, I see two issues with this. One, as soon as we go into some more technical, literary or just uncommon words and phrases, there will be hiccups when we either get our whole rhytm broken by a word we don't get or we misread a word only to realize three lines later there was an issue somewhere, and we have to go back look for it. A closely related thing is that if there are any names, especially complicated and/or foreign ones, we would need to get used to them before we could go on smoothly.
Second issue, I'm not sure how it would fare in regards to internalizing and retaining the information we read. When I read, I tend to imagine what I read in my head, and there would likely be issues with dialogues and some action scenes that are designed to flow fast or slow, as they would either feel totally rushed or weirdly faster than the prose and structure makes us think they should.
It's probably just a trade off. You could make it amazing if you used it well, but actually using it well is a challenge on its own, and it would most likely not be for everyone.