I think the XCOM 2 example is a good illustration of the kinds of invisible lines that gradually get drawn around a long-running series over time by players' expectations. People expect the next game in the series to play fairly similarly to the previous ones, so if the designers take it too far in a different direction, the players recoil. It doesn't even really matter if the new direction is objectively better. It's just a "New Coke" problem -- people expect Coke to taste a certain way.
In the case of XCOM 2, I don't think timed missions were by themselves a bad idea. It's just that they were different enough from what people expected from an X-COM game that they didn't fit. They pushed the design of the game across one of those invisible lines.
The time limit was a bit too arbitaray. I think instead of failure, a time limit on extra rewards is more favourable. The Xcom enemy within expansion did it right by making a time limit hidden (with sound clues) for the extra "meld" reward. You could split your team and hunt for the reward, but risk trigger multiple enemies, or forfeit the reward for safe play. The player is in the control seat, not the game.
In the case of XCOM 2, I don't think timed missions were by themselves a bad idea. It's just that they were different enough from what people expected from an X-COM game that they didn't fit. They pushed the design of the game across one of those invisible lines.