Conversions... what's the problem?

the main PRACTICAL disadvantage is that the bottom bracket will be lower. The solution is to use short cranks, but you'll get less leverage and so it will be harder work.

More misinformation, leverage and the perception of 'harder work' relate to your chosen gearing.

There is also the fact that the geometry will be slacker, which will affect the handling— but this is a matter of personal preference.

True, a road frame is designed for the road, which is better for the road than a track bike, which is designed for the track.