I think using 'every other craft skill or labor' is not a great example, because every other craft skill or labor (excepting teaching) is not giving other people experience. it's a bit of a power-creep issue, IMO. If I spend 2-3 seasons getting my teaching up to 4, I now get a +2 to every book I write. it also lets me write a tractatus on teaching, which makes the rest of my covenant get better book writing - not just the 3 other magi, but all 4+ companions and any 20-120+ covenfolk we can convince to write a book. While it does let the aged archmagus write his final opus, it also creates a reason for every covenant to write EVEN MORE books.
If you like the current rules supporting a covenant pushing every covenfolk to learn magic theory and write tractati on it, (and now adding teaching to it as well) then your rules certainly cover that. Unless you make it so that those rules don't apply to tractati.
Again, I may want to suggest requiring additional seasons to add extra bonuses beyond baseline, as someone 'refines' their book or edits it for clarity and ease of understanding, which still lets someone do an end-of-life opus... feels good to have someone working on their last bit (or maybe a required adventure to test and clarify some obscure theory of theirs in the book) .. spend 1-2 years going into editing and testing things...having some of their former apprentices read sections to reply with comprehension.
by now it should be clear that my problem with the library rules aren't summae, but tractati. 
But if you are looking for something more realistic that lets people work for better books suited to a Master of an Art, instead look into letting them spend extra seasons and time to get those bonuses. Just giving the bonuses by default may feel realistic, but also leads to a lot of side-effects. In modern society, just look at how much work writing a thesis for masters degrees or PhDs take.