It's both. You're not telling me that players like Lovren and Matip couldn't be better coached. I don't have huge faith in either of them, but a different coach would get a better performance from them. Have a look at our defensive play in general under Klopp. EVERY centre back has failed to some degree. You could only really say that Moreno and Milner have progressed as defenders, the rest have regressed. Matip, Lovren, Sakho, Gomez, Karius, even Clyne.. all performed better previously. Like I say, we need to buy, but I don't think it's completely down to poor players, that every single centre back we have has underperformed/failed under the same manager.
It's like when Evans was here, every centre back performed badly and despite buying mostly average/poor players, some of them were better before they came here, yet every single one of them struggled under the tactical system and lack of organisation. Mark Wright and John Scales were the pick of the bunch and neither of them completely succeeded here.
Gomez played everyone onside at Spurs for one of the goals, he's a kid learning the ropes, so these things happen, but it was such a basic fundamental mistake (looking along the line and still not stepping out inline), that I can't help but point the finger at the organisation. Things like not playing to the whistle - you're taught that at grass roots level, so if we've stopped doing it now (Matip, Lovren and a few others were repeatedly guilty of this at Spurs), then is that just retarded players or poor instruction? When they're all doing it, it stops being an individual problem, it's a team problem and then it becomes a methodical/coaching problem.