1) Investors aren't idiots when it comes to growth. No one expects today's growth rates to stay constant. Growth decelerates over time.
2) You can't take averages of revenue and growth across lots of startups and use that as your model. Here's an example with two startups:
* Startup 1: $4.99m annual revenue, grew 5% last month.
* Startup 2: $10k annual revenue, grew 145% last month.
"Hey look, if you average these growth rates out, you have a combined $5m in annual revenue growing 75% monthly. That'll be >$4b in annualized revenue in a year!!1!"
No, it won't.
The reason investors value high growth in young companies is that growth rates are an okay proxy for a lot of valuable things: product-market fit, execution ability, go to market strategy, etc.