The internet has changed things on this front a bit too.
Consider back in the 90s, DJs might have a very similar sounding set for a good two or three months, having it evolve with new tunes appearing over time. Now, nobody can be seen to play the same tune twice and release schedules are mental busy. So way back when, DJs had more opportunity to get to know their records; swerve the key clashes, find the cue points, get a flow etc. Now things have to be a bit more instant, hence the leg work that goes into setting up mixes, and why some DJs have ‘human filters’ going through new music for them.
Put simply, DJs who prep sound better, but if you’re not recording it for other to listen to multiple times, don’t worry too much about it, just enjoy it.