All addons count for the start-up checking process, because all are also loaded by game no matter where they are stored. At least several of us could confirm that this is the case during tests.
Please take a look to the following bug report and vote there so that the issue gets priority. In my opinion it´s a serious one that was probably missed because devs may only perform tests with official content as you would expect, but it could even prevent official content to load at some point as that content also increases periodically with the new SUs and WUs which are released. We are indeed quite close to the limit right now so fixing this is relatively urgent.
Cheers