[olddog]

Assuming the engine is cold, when you removed the hose, the thermostat would be closed. The water may well drain slow due to no air allowed to enter the engine via a close T-stat.

If you removed the water temp sensor, that would have allowed the air in. If it still drained slow, then maybe there is a problem.

I'm thinking the water still has to flow through the water pump impeller. So it is not going to drain as fast as the radiator. So it may depend on how slow you are talking.