Base on what? If the strategy is to counter Kamui, the clones would be in places they need to. Your repeating the same defeated argument. Obito can't teleport himself and then open Kamui again to use Shirukens, without Hiruzen reacting. Your premise has Obito with zero intangibility during that kind of process. NO Obito cannot be all over the battle field and do these things your suggesting, please follow manga showcase of Kamui usage.
I added Manga Intel just to see to see how many people will underestimate the Professors intelligence, like your doing right now. Hiruzen easily figures out the mechanics of Obito's S/T, much faster then Minato. Especially since Hiruzen fight style is similar to Kakashi via use Clone for intel (Orochimaru implication). Konan
sends paper towards Obito's direction jutsu in case he wanted to teleport away[
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]. What Hiruzen most definitely has jutsu that comes out faster then 2 secs[
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]. Even a blitz will only take a sec.
Full Speed Kamui is irrelevant when Clones Feint are there plus Physical contact w/ Shadow Possession is instant.