So he would have a crippled (by Scotty) ship in III, not be in IV or V at all and have the same scenes in VI, maybe. By then, people would have thought "Sulu? Sulu Who?" and a different captain would have been helming the Excelsior. If Shatner did this on purpose, he did Takei the actor a big favor.
Takei did not care. From the moment he thought Sulu was going to get his own ship during the TWOK production, he's felt the need to harp on the idea....even though next to no one ever expresssed widespread interest in a solo Sulu anything
As noted days ago, the spin-off notion was dicey at best, and there were a wealth of failures giving enough reasons why a Sulu series and/or movie would not work. TOS works best when the character triangle/chain of command is the driving force of the Enterprise adventures, not splintered supporting characters lacking the "it" factor (and deliberate character development) of the stars.