Guide? As in the blue power bar? I can ace without it because I know how to time it. But I think that bar is necessary on the serve, because the mechanics are not perfect and you should know exactly how much power you are putting into it. As you noticed, I don't use the placement marker, I hate that thing.
And obviously I told the devs that I am noticing it more on higher difficulties. But, on Pro you can ace just as easily with a elite server/above average server. I was acing the CPU with ease on Pro with Monfils, I had 16 in the first set. Just like in the videos, the full power green to outside or inside causes the CPU to stumble.
I'll say again, I deserve more benefit of the doubt. And I have no problem uploading videos of me doing it on Pro if time permits. Note: The dudes bragging about high ace counts on Facebook are playing quick matches/matches online (PS4 I believe) and they are boasting about unstoppable serving. Online defaults to pro difficulty, so it's overpowering and unrealistic with human vs human and human vs CPU.
I've clearly demonstrated in the Human vs CPU video how ridiculously easy it is to get aces down the middle (3 out of 4 points won in grand slam against a 90 overall), and I'll say again: I have had entire sets where every point on my serve with the exception of 1 or 2 are aces. It is literally gamebreaking. The game is no fun, and unbelievabley easy and unrealistic when that exploit exists.