“What I mean is that when they announce the molad in shul they assume that the moon moves at a constant speed. However it doesn’t. But we do it this way for convenience and simplicity.”
Its not just for “convenience and simplicity” the whole calendar is structured on the average speed. It wouldnt be possible to produce a calendar based on the actual molad because it varies within each cycle and cycle to cycle. EAnd forget about getting it to fit with the solar cycle , which isnt just convenient but a necessity due to chodesh haaviv.
The molad announced in shul is the one upon which our entire calendar is structured. while it isnt the “actual astronomical” molad or “molad ha’amiti” this sint because anyone is “rounding” anything