Here's my theory on excellent beer: It's a function of a lot of specific process characteristics that, together, add up to excellent beer. Start making shortcuts and the more you do that, the less excellence your beer will exhibit.
That's why the "what's most important" threads and arguments are not that interesting to me. It's all important! That is, if you're trying to produce the best beer possible given your system and constraints.
I've followed an approach of continuous quality improvement in my brewing history. Every time I brew, I try to do something better. Reduce oxygen exposure HERE. Do a better starter THERE. Adjust my crush. Time my additions better (for reproduceability). Hops. Racking. Purging kegs. Reducing O2 exposure on racking. Etc. etc. etc.
Try to do something better. Every. Single. Time.
It adds up. Make it your mission to keep learning. You clearly have identified water as a place for improvement, so work on that. Read, read, read and see what you can learn about it, and begin to improve your brewing water. Once you think you have that settled, move on to something else.
Maybe....yeast? Are you pitching the correct amount? How do you do starters? Is there a better way?
Same with fermentation temp control. Are you doing that? Can you do it better?
And so on, and so forth.
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If you view this as a journey, it can be very enjoyable. Tweak this. Play with that. Adjust over here. Learn. Then learn some more. Whatever your "conventional wisdom" is, challenge it. Look for evidence there's another, better way. And if it appears there is, adopt it if you can.
Don't assume you're missing just the one thing. You're missing everything, if you're not continuously trying to improve your process.
Good luck, and whatever you do, enjoy the journey. It's a very good journey.