I wonder if more companies use web domains as "investments" aswell

There are domain name investment companies, yes. HugeDomains owns over 5 million domains!

As for product companies, like Ramp, buying domains as an investment is generally a terrible idea. Domains are not liquid, the (hypothetical) $5 million that Ramp paid is not a price Ramp could achieve when selling the domain tomorrow. The previous owners owned Router.com for over 20 years before Ramp came along, willing to pay a lot of money for it.

Sometimes a company will buy a domain, use it, shut down whatever it was, then end up with the domain on their balance sheet for years, even decades, before someone tracks them down and offers to buy it. In those cases, the company can make money off the domain, but for every time that happens, there’s thousands more domains on balance sheets that nobody wants to pay a good amount for.

More broadly, domain name investors make their money by buying lots of domains and holding them over the long term, making their money from the very small number that sell. Part of why good domains are so expensive is that 1 sale needs to cover the cost of hundreds of even thousands of other domains that don’t sell.

Domains investors (or squatters, as one may call them) have been around since the beginning of domains.