So basically when I rely on visual cues i.e. wait for the end of an animation and then try to punish or do something when it finishes I might be already too late frame-wise because of the visual delay, am I getting this right?
I may be reading into phrasing here but I wanted to back up an highlight this specifically and pull it completely out of an online context.
The main reason I bring it up is if you are saying you are waiting for your
opponent's attack animation to end, that's actually not when you want to be counter attacking, and depending on the attack and lag sources involved, could attribute to you getting beat out against someone going for more buttons.
If you are visually trying to queue off something, you want to start countering the moment your block animation ends, which can be significantly sooner than your opponent's recovery frames end. If you wait until they are winding down their animation, then what you are doing is throwing away your advantage frames, and waiting until you both return to neutral. At that point whatever character has the fastest button is going to be the one with the best situation.
Add any lag sources, and you may be in worse disadvantage because you are going off of what you see, where as they know the perfect timing to press a button after whatever it was they did; since they do it all the time.
It's not particularly easy or not natural for a lot of people. I don't follow my own advice, I started watching my opponent exclusively way too many years ago. I think it's too late for me, but when you are being forced to block, try to pay attention to what they did, and when your character actually frees up from blocking.
I don't know if that has anything to do with stuff you were picking up on but it theoretically could. The game will delay your inputs 3 frames (as of NRS's GDC network keynote during IJ2) and that is on top of your reactions. So if you waited until their animation ends as a habit, online you are basically going to be -3 every time you block all day long.
Eventually you will start to memorize/practice moves and the right time to counter instead of trying to reactively figure out when something ends, but again that takes time with a specific game.