I dunno, I think you're trying to split hairs if top 20 isn't "very popular".
But I don't think the comparison you're trying to make works, because then isn't now.
In general, in order to convince someone to leave their current tools, you have to not only be better but a lot better. As in, you need to offer the entire feature set of the old tool plus something else compelling enough to overcome the network effects (ecosystem + years of experience + job prospects) of the prior environment.
So when C++ came on the scene, they had to compete against ~20 years of accumulated legacy systems and language history. Rust had to compete with 50 years of legacy systems and language history.
Moreover, developer expectations are a lot different today. Back then, C++ was what, a compiler and some docs? Python was an interpreter and some docs? Maybe an IRC channel? Today, it's not enough to reach 1.0, you also have to deliver a package manager, robust 3rd party library ecosystem, language server tooling, a robust community with support for new devs, etc. So timescales for language development are getting longer than they were back then.
Also, I don't know why you've chosen "very popular" as a metric. Very popular isn't something a language needs to be, it just needs to be big enough to sustain a community. Being top 20 within 10 years is certainly in that realm. You can see that other language communities have existed for longer and are much smaller. And anyway, the entire developer population today is much larger than it was back then; you can have a small percentage of all developers but still large enough to be robust. I don't know the math, maybe someone can figure it out, but I wouldn't be surprised if 1% of developers today is inflation adjusted to like 10%-20% of developers in 1996. So Rust is probably as big as it needs to be to sustain itself, it doesn't have to be a "very popular" language if that means being in the top 5 or whatever the threshold is.