We know for a fact that both Star and the Jet pilots confused the Near High-End jumping out of the water as being Shigaraki. If the Near High-End wasn't comparable to Tomura, who they've seem propel himself with enhanced strength, they would've instantly noticed it wasn't him.
They were heavily focused on Shigaraki's location as well, who even admits that he needed to wait for the right time. To early and they'd notice the switch. A second's delay would've been a fatal error. The Nomu being incomparable to Shigaraki's speed makes this entire plan fall flat on its face.
Not only that. But we know for a fact that Tomura's physical durability is unchanged, as he and the Near High-End takes comparable amount of damage from Star's attack. It would be extremely weird if Tomura's speed is faster, while his durability remains unchanged. His physical strength is unknown.
While not impossible, I'm not alright with betting on an assumption that he's faster, without a statement or showing that he is indeed faster. The reason we have Incomplete Shigaraki and Complete Shigaraki, is because there is no evidence to suggest 75% Shiggy and 98% Shiggy are different from each other.
The changes to Shigaraki's body began happening after the battle with Star, as his body adapted against the "singularity".
As Garaki stated, the hardware that is the body needs to adapt to handle the increase in memory, which is the Quirks. Shiggy's body wasn't fully fused with the AFO Quirk, which is what the percentages are.
The closer the AFO quirk is fused with Shigaraki,
the higher the percentage. Once he reached 100%, his body began to change. His body was evolving to handle the evolving Quirks. This is my reasoning for why Tomura during his fight with Star shouldn't be faster/stronger than his battle in Jaku.
Basically. The percentages aren't a measure of Tomura's power/strength, just a measure of how much the AFO Quirk has fused into his body. Once the fusion finished and it became one with Tomura, his body began to evolve to handle the massive amount of Quirks.