I know of an apartment unit, just replaced last year, that suffers this problem. The liquid line is indeed much hotter than it [should be], given the 70-degree outside temp that was present when I looked at it. I have no quantitative measurements, but just comparing this apartment system to my system at home, whos liquid line doesn't get 'hot' until the temp approaches 95 outside.
Inside, the tempurature delta cannot possibly be anywhere near 20degrees.
BUT... The conndenser unit is the kind that blows the hot air out right above the intake, and I know it's sucking all that hot air back across the coil; THIS would also account for a hot liquid line.