But once you have repeatable steps and that are good (water, quantities, temperature etc.) the grinder becomes the most important piece even in espresso.
I would say it's most important for espresso, at least in espresso machines that do everything else well. You essentially control the duration of the pull via the grind, and the taste of the shot comes predominantly from how long and hot you pull it.
As you said, once you are dialed in, really the only variable I am tweaking per bag of beans is the grind.
Not really, almost everything else matters more. Bean quality and water quality in particular are at the top of the list. Good beans bad grinder > bad beans good grinder. The grinder is the last place to look, even though it does matter.
The mistake you’re making is that not all variables are under your control.
Getting better and better beans is very hard. You’re stuck with what is available. You’re stuck with what water is available (if you’re a reasonable person). You’re stuck with the local roasters.
So of the variables you can control, the grinder is the most important piece of equipment you can buy.
Of course they are, don’t be so helpless. Getting good beans vs Starbucks is trivial. You’re obviously not limited to local roasters, google “specialty coffee delivery”, it needs to rest for around a week anyway. As is getting filtered water (in-line under your sink for less than $100, filter pitcher for a fraction of that) and saline drops (you can buy them for next to nothing online or mad-science your own for even less). All of those things will make a huge improvement compared with a better grinder.
Again. Grinders can make a difference, but they’re the last step in the chain. Do everything else first.
The other mistake you’re making is thinking people haven’t tried all of this and this is new information to them. And that trying all that results in a product that someone else prefers.
The fact is, there is a certain level of spend needed. If you’re not making espresso, this is very low these days. You can get very cheap, good gear. If you are making espresso, you’re spending several hundred minimum. Although you can lower your spend quite a bit if you’re willing to hand grind for espresso.
As you said, once you are dialed in, really the only variable I am tweaking per bag of beans is the grind.