Is ARR actually a distraction for early-stage SaaS?

Just read a piece by Sam Shank on a16z. He argues that for early-stage B2B SaaS, focusing on ARR might be a mistake because it’s a trailing indicator.

Instead, he points to Slack. They found that once a team sent 2,000 messages, there was a 93% chance they’d keep using it. That one "usage" number became their obsession, not the revenue.

I see so many founders (myself included) staring at dashboards with 50+ KPIs, what Shank calls "metrics slop." We’re measuring everything but understanding nothing.

If you had to delete every column in your spreadsheet except one to ensure your startup survives, which one would you keep? Is it still ARR, or something deeper?