For this issue and for JS execution maybe. But there are so many features in modern browsers that the cat-and-mouse game of waiting for vulns to know you've hit all of the places for fingerprinting and other deanon is untenable. Couple that with extensions TBB bundles by default, e.g. https everywhere, and the surface area is even larger.

TBB has value for general browsing, but secure browsing needs to be by document format as much as implementation. Right now, the only reasonable option for onion services is to have their site browsed via the large, feature-rich bundle. Unfortunately, it requires a good bit of funding to build a document browsing platform of any size so I definitely understand the current practical approach.