I was using those two as an example of how players can play a key part of a promotion but still be let go as they are deemed not good enough for the level you've been promoted to. To be successful in the PL you have to be ruthless. And for clarity, I was talking specifically about Armstrong's situation last summer. He'd already proven then that he was not at the level required for PL, he lacks the physicality and technical ability to be effective. He should not have been relied on as much as he was in the first half of the season nor given a new contract. As said elsewhere, that was the time to cash in.
This summer represents several new points of debate around Armstrong:
Firstly, does he fit into Will Still's system? If not, then the rest is moot and we can move him on.
Secondly, having now absolutely proven that he's not good enough to be a premier league player, does he have the required motivation and confidence to be as effective in the championship? His loan spell for WBA suggests maybe not.
Thirdly, if we do use him on a "2-year cycle" as you put it, will we not just be in exactly the same position in 2 years time?
In my opinion, he's still a very good championship player that deserves to play for promotion-chasing championship teams but unfortunately is not good enough to play in the league above. With that in mind, if he suits Will Still's system, we should keep him until we get promoted.