Of course teams became better at drafting over time: there is much more tape on prospects, much greater use of analytics, better understanding of what the teams can improve in prospects by coaching and physical programs. The reason why the draft is still far from certainty is because the talent pool has become became truly global and you have to somehow compare euros from the weak professional leagues against American players in the NCAA etc.
Also, the NBA stars have become much more skilled than before: they have to be able to score, defend on the perimeter, hit threes, be good passers, maintain their body for the entire season and, often, The international tournaments... In the past a good size and athleticism alone were a much better predictor of future prospects. You did not have to guess if this center could develop a three point game or that wing could become a good playmaker. Drafting teenagers into the hardest professional league is an incredibly hard job and, I think, those doing it should be appreciated a bit more.