Not necessarily. But even then do you seriously think a jinchuuriki changes it so much 1/2 a tailed beast can match the chakra of 4 tailed beasts. The nine tails is just a different beast compare to the others.
Bijuu have no Shinobi training, so they can’t manage their chakra nearly as well as someone like War Arc Naruto could. Think about it like this: a normal Bijuu would have to spend let’s say 1 million points of chakra to produce a Bijuudama, while a Perfect Jinchuriki with chakra efficiency on Naruto’s level would only have to spend 100,000 chakra points to produce a Bijuudama because the latter knows how to manage their chakra better.
That’s the only logical explanation I can come up for to explain why Obito said a Perfect Jinchuriki is much more powerful than the Bijuu itself