It's probably worth noting here that 360,000 wasn't the forecast, and is just a number that has been pulled from one of the usual extremely speculative crayon reports councils like to create for if they ever find a money tree.
The actual forecasting done for the station is available
here. (Using the revenue forecasts to save everyone getting the calculator out):
As can be seen forecast passenger numbers were 160,000 in the first year, which was for the assumed opening date of 2016. Given what has happened since with Covid, the drop in forecast passengers lines up relatively well with what has been seen across the country, especially given Marsh Barton's forecast traffic was largely reliant on people commuting to work, before new developments open, which they still haven't, and Marsh Barton has been hit very heavily by closures of businesses, especially after Covid.