Caffeine pills it's a bit easy to unconciously take too much and get all jittery, and it's not really spread out enough.

Optimal consumption of caffeine seems to be a decent-sized initial intake, then smaller doses over time to maintain (eg take a few more sips). There's no good way to do that with pills.

How confident are you in the dosage in each cup of coffee?

Fairly confident, within 2x or so.

But it barely matters, it's not like I'd inject the whole cup into my veins and then see what happens.

If the caffeine was too high (within reasonable variations), you'd notice and slow down consumption before it mattered. If it's too low, you can just drink more. You can do it by feel, which is I think what just about everyone does.

Some of it might be placebo, but if so I'm not sure it changes anything really, since the goal is just to feel a certain way anyway.

Or you could drink an energy drink/sugar free cola instead.

No, the chemical compounds of those can have quite adverse effects. Sweeteners are linked with insuline problems.

It’s the reverse. People wanted decaffeinated coffee and the TCE stayed for the ride.

Whole coffee has a well established safety record for long term use. Pure caffeine at the doses coffee drinkers use, less so. There might be other unidentified chemicals in whole coffee that interact with the caffeine in some way to modify its safety.