It was true, and it was what made Google Chrome popular in the first place. Internet Explorer and Firefox were dead slow to start at the time while Chrome started instantly.
We just don’t know how bad slow browsers can be because all others have caught up.
That was a funny period of time because you could very transparently see the clear application of a corporate team that was tasked with improving the “startup speed KPI”.
During that time IE startup time went from a dozen or so seconds to also instantaneous. It was even faster than chrome sometimes. But that was just the startup. The application wasn’t ready to accept any user input or load anything for another 10 or 15 seconds still. Sometimes it would even accept input for a second then block the input fields again.
It’s the same mentality all those insanely slow webapps do when they think some core react feature for a “initial render” or splash screen etc will save them from their horrific engineering practices.
Google did a great job communicating Chrome's improvements over speed (both with startup and prefetch) and reliability (isolated and sandboxed tabs) during its launch. When you saw it, you knew that it was basically game over for any browser that had chosen to stagnate until then. They destroyed the competition.
I think Google gained more users with its aggressive advertising campaign than with its speed (except for power users). If someone used a Google product like search, email or youtube in a non-google browser, Google would always show an ad encouraging them to switch to Chrome.
At the time, the argument for Chrome was that Firefox and IE were bloated and their memory requirements were too high.
A system with less than 64 Megabytes of RAM (most computers of the time) would have to lean heavily on spinning rust virtual memory, making everything slow.
However, since then Chrome has become one of the biggest memory hogs that people commonly run.
I don't think lean memory use was the biggest claim Chrome had made. That was the game between IE and Firefox. Google had specifically promoted faster startup times, faster web browsing experience, and tab isolation / sandboxing so a crashing tab wouldn't bring down other tabs with it.
Netscape 6, which was released in 2000 and based on the Mozilla Suite (now SeaMonkey) recommended 64MB of RAM. The Mozilla Suite was the basis of the Phoenix project (later renamed to Firefox) and they shared the same technological underpinnings: Gecko engine, SpiderMonkey JS engine, XUL interface, XPCOM, etc. Phoenix/Firefox was about using the Mozilla technology to deliver just a browser, independent of the suite, with aim of being lighter weight. So while Firefox didn't exist yet its heavier predecessor did.
We just don’t know how bad slow browsers can be because all others have caught up.