If his awakening makes everything invisible, it would be overwhelming, especially if he takes the fight to uneven terrain or into a woodland where you'll run into trees.
Maybe his current invisibility is still a problem for most characters with Observation, because they can't use it constantly for a whole fight without losing concentration. And maybe it's still hard to know the exact timing and position of his sword without seeing it. You feel his intent to slash your right arm, but the exact timing of the swing might be tough to read, unless you're Fujitora who's practiced it. Most characters with Observation still use their eyes to help them keep track of things.
He could also remove intent from his attacks until it's very close to landing and his opponent is already out of position to guard or dodge. If he swings his sword with the intent to cut, if Zoro doesn't react the sword continues and cuts Zoro. If Zoro reacts to the intent and raises his guard to block, Shiryu's attack becomes a fake attack and he does a different attack instead, but because Zoro's sword was already in position to block the first attack, so although he senses the new attack's intent, he can't move to block it in time. Now Zoro could try to read Shiryu's intent of "I'm swinging my sword like A, but if he moves to block I'll change it to B", and because Shiryu's mind is already poised for moving to attack B, he knows that B is coming if he reacts. I'm not sure Zoro even could read that, if Shiryu is really intent on landing A until he sees Zoro move to block - his intent for B isn't there to read.
But say Zoro can read it.
Well, then Shiryu can add forks in the decision-making. "I'll swing A, but if he reacts I'll go for either B or C", where B and C are sufficiently different that the opponent cannot move to block one and then change it to the other fast enough if they guessed wrong. Shiryu can hide his intent by not even knowing for himself which one he plans to do. He can choose something external to make the choice for him. For example, he could decide if Zoro goes "ugh" he'll go left, if he goes "tch" he'll go right. Even if Zoro can feel that A is being thrown and that Shiryu is considering B or C as a follow up, he can't read minds so doesn't know that Shiryu is deciding based on what noise he makes. Or if he does somehow eventually figure it out, Shiryu can use something else, like whether Zoro's left or right sword moves first.
Any of those tactics to throw off Observation would make his invisibility still retain some advantage.