As a counter-argument, Canon Japan posts
a list of support period for its products. Support expiring roughly seven years after discontinuation, and current products are marked as "undetermined" (未定)。 (The page is in Japanese, but you should be able to make out the dates without Google Translate's help.)
According to that web page, 40STM, EF-S 60, 85F1.2L, 200F2L, 70-200F2.8L(non-IS), 300F4L, EF-S 18-200 all have support expiration dates defined, a good indication that they are indeed discontinued. But 70-200F4L II, 85F1.8, and 800F5.6L do NOT have expiration dates attached to them.
Another data point from Canon Japan is their catalogue
of EF lenses, which show "low inventory" (在庫僅少) or "discontinued" (販売終了) on some lenses. 40, 60, 85F1.2L, 200, 70-200F2.8L, 300, 18-200 all have either "low inventory" next to them, while 70-200F4L II, 85F1.8, and 800 do not have anything attached to them. So this list correlates cleanly with the earlier list, and not with Canon USA's list of "out of stock" items.
tl;dr: I am highly skeptical about 70-200F4L II being actually discontinued. Considering the extreme supply constraints on RF lenses right now*, a more likely explanation is that Canon is using all of its manufacturing lines to push out RF lenses, and they don't have a timetable on when they'll get back to producing the poorer-selling EF lenses.
* Last weekend, a sales rep at one of the major camera shops in Tokyo told me that he doesn't have any RF lens in stock except RF 50 STM. Yow.