[Marcello]

The idea behind the russian barrel fired ATGMs was to provide a limited, accurate long range capability against high value targets. This was very expensive, as I noted, but as long as it is limited (only a fraction of the tanks fitted with it and a limited number of rounds) still easier and cheaper than developing and deploying on every tank all the technologies necessary to ensure comparable performances with conventional rounds (very sophisticated FCS, tighter tulerances in gun manufacturing and what not). I also suppose that especially early on it provided capabilities that it would have simply been impossible to match otherwise.
The scheme basically makes sense only as long as you use them sparingly. Otherwise it is more cost effective investing into high end FCS and such.