The trouble with programmed drums isn't that they sound bad; it's that they sound too good. The micro-imperfections that make a real drummer recognizable as a person are exactly what default MIDI grids strip away. I spent about six months in Ableton learning to put those imperfections back in, and this is the working shape of what that took.
Start with why libraries fail on close listening. A sample library is a grid of discrete recordings: this drum, at this velocity band, round-robined so consecutive hits don't repeat a file. Every one of those words is a compromise. Velocity bands mean a hit at 96 and a hit at 97 can jump between two different recorded performances, while a real drummer's dynamics are continuous. Round-robin means variation is random, and a drummer's variation is anything but: it correlates with effort, position in the phrase, which limb is doing the work. The library plays back perfect little photographs. A drummer is a moving picture.
So the first stretch went into velocity, not timing. I sampled live sounds at a range of textures myself rather than leaning on a library's bands, because the thing I needed wasn't more dynamic levels. It was the character change between them: the way a rimshot blooms differently when it's hit tired. The lie a velocity layer tells is that loudness is the variable. It isn't. Effort is, and effort shows up in tone before it shows up in volume. Once the samples carried that, velocity curves could be drawn against the phrase: a right hand that droops a few points across a long run of eighths, accents that recover, fills that spend energy the following bar has to pay back.
Timing was the second front. Humanization as most tools ship it (uniform random offset per note) is white noise, and ears identify white noise instantly. Real timing error is correlated: a drummer drifts, notices, corrects, overshoots slightly, settles. I ended up scripting the drift instead of randomizing it: MIDI nudged by a slow wandering curve, with the correction built in, so the grid breathes in one direction for a phrase before it leans back. The keyword is believably: drift without correction falls apart, correction without drift is just the grid again.
The metronome itself was the last thing to break, on purpose. Even with humanized notes, a mathematically constant tempo underneath reads as a machine within a few bars. So the tempo track moves: a couple of BPM of push into choruses, a settle after the fill, the kind of shape a band produces because four people are listening to each other rather than to a click. It's a small thing that changes everything above it, because now the "errors" in the notes are errors against a moving reference, which is what human timing error actually is.
Six months, roughly in that order: samples and velocity first, drift second, tempo last. Fast enough, in the end, to keep up with the writing rather than replace it. If you're starting the same project, the ordering is the advice. Everyone reaches for timing first because timing is what tools expose. But a perfectly timed part with honest dynamics sounds like a drummer having a good night; perfectly sampled dynamics on a naive grid sound like a robot with feelings. Do effort first. Timing is only convincing when there's a body implied behind it.
The test that mattered, in the end, wasn't technical. Nobody who heard the drums on a drunkgiantbird track asked what library I used. They asked who the drummer was.