People does not understand that Zoro using Enma count already as a power up. Having a stronger sword should count as a power up. Zoro get stronger not only by using haki or special technique (ashura) but also and more importantly by getting new swords.
So, I think that saying "this is base Zoro" is fundamentally wrong.
The fact that Sanji is using IJ more (still from the attacks he did after Queen power up I would not say that he is spamming IJ for now) means that he can use it now more frequently without issue. It's like DJ after the time skip. Even Luffy using more G5 means he is getting more comfortable in using that power up.
In other words, while Zoro seems like is always in "base form" in reality he is not because he already use new and more stronger swords and the power up is more subtle and concealed. Meanwhile Luffy and Sanji show their power up in a more obvservable way.