The thing is, almost all the trivial comments can be easily automated. That would both give the junior dev quicker feedback before even raising the review, and save time for everyone.
Junior code is not usually more complex because of bad naming conventions and inconsistent styling and related issues that tools can help with, although of course these don't help its readability overall. Rather it usually has control flow that's far too literal a translation of requirements leading to an exponential explosion of paths, insufficient and/or over-eager error handling (often both at the same time), poor representational choices leading to inefficiency or more special cases, and so on. None of these can be effectively automatically detected.
