Garou clears the distance quite easily. At the speed they are moving at (Speed Equalization means that Shigaraki's speed is reduced to Garou's speed), it takes Garou less than seconds (0.00307488 milliseconds if you care) to go from 4 kilometers to directly in Shigaraki's face. Garou will fly over Shigaraki's Decay wave if he decides to start with it and when Garou sees Shigaraki's hand touch the ground and the ground underneath starts to decay, he will avoid coming into contact with Protruding Limbs. He dodged Shooter's
Poisonous Arrows when he knew that they were poisoned, shouldn't be any different with Protruding Limbs. Rivet stabs are a toss up between Garou dodging or deflecting them, so he can absolutely try to deflect and get dusted like that.
As I said in my earlier message, when Shigaraki's Decay go all the way down into the ocean, Shigaraki's movement options are limited compared to Garou's. The means of Shigaraki's Flight and Acrobatics (shown below) hinders his fighting compared to when he's fighting on ground.
Flight (Can freely move in the air with his Quirks.
Can propel himself through the air using wind pressure if he cannot use his Quirks)
His Acrobatic feat is really just Lifting Strength feat (see
this), and I don't know what his "complex acrobatics" he's shown. Shigaraki's
Flight isn't much either. Shigaraki has to keep his momentum to maintain his flight, which means that Shigaraki will fall like a wet noodle when Garou breaks his bones with CDFSF.
Shigaraki doesn't have much when it comes to anything that allows him to hit Garou from range. No one answered (or at least Therefir didn't respond) how Shigaraki is hitting Garou when he has
Water Stream Rock Smashing Fist,
Instinctive Reaction, and
Analytical Prediction. In this
Key, his skill massively upscales from his previous keys who is equal to Bang and Atomic, who in turn is higher than his students, who can cut thousands of attacks (1800+ to be exact) with their eyes closed and sensing intent (Emerald and Phoenks). Shigaraki isn't creating that many projectiles.
Mid Regeneration does circumvent Garou's CDFSF, it takes time for it to work.
Here, when Shigaraki's arm is destroyed.
Still healing, then
still healing and now it's back. When Garou's every punch is breaking bones, it'll put a lot of strain on Shigaraki. And eventually, Garou will absolutely figure out Shigaraki's Regeneration's weakness,
as he did with Sage Centipede (or just reading that Shigaraki is trying to protect his head) and start to target his head. RASRF would break Shigaraki's skull and tear apart his brain.
When Shigaraki moves on to his infinite growth, Garou will prioritizing dodging and look for openings, which he will find when he evolves and adapts to Shigaraki. When the equation is getting touching = death, it doesn't take a mathematician to know the product. CDFSF actually hurt and tax Shigaraki even more since Super Regeneration has to heal far more damage than before.
Shigaraki can definitely win if he touches Garou once and Shigaraki's Wave-Motion Gun absolutely blazes his *** (depending if Decay works through it), it's just that he needs to rely on Garou making a mistake to do that. Garou isn't prone to making mistakes like touching Protruding Limbs or not focusing on Shigaraki's
Regeneration to lose to Decay more often than not.
P.S, Is Shigaraki's big *** even tall enough to stay above sea level to not drown? The mountain will be nothing but sea and sky after Shigaraki uses Decay.