Braising is not “slow roasting with liquid”. It is a specific transformation, and knowing which one tells you when a dish is done.
The change you are waiting for
Tough cuts are tough because of collagen. Below about 70°C collagen just sits there. Above it, given enough time in the presence of water, it converts to gelatine — which is why a shin that was rubbery at two hours is silky at three, and why the sauce thickens without any flour.
That conversion is slow and temperature-sensitive. Hotter is not faster in any useful sense: at 200°C the outside of the meat dries and tightens long before the middle has had its three hours, and you end up with strings in a thin sauce.
What that means in practice
Keep the oven at 150°C and the liquid at a bare tremble, never a boil. Keep the lid on: the point is a humid environment, not reduction. Reduce at the end, with the lid off and the meat lifted out, when you can taste what you are reducing.
And stop testing with a timer. The dish is ready when a spoon goes through the meat with no resistance — three hours is a prediction, not a rule.