Earlier quoted context omitted.
What OS do you think you were running in 1996?
Sorry, it was 1998. I’m pretty sure Mac OS 8 had drop shadows but even if it didn’t, I took that machine all the way to 10.4 and every version of OS X had drop shadows.
I don't think OS X is a good example of your point because resizing windows was incredibly sluggish for a long time. I always figured it was somehow due to the combination of live resizing plus ubiquitous compositing, but I never understood why it was so slow.