What are the issues with Linode not having an ASN?

My comment was more to indicate the overall state of their own network, which didn't exist at all until very recently.

Linode may be 14 years old, but they've only been running their own network for a year.

If they don't have an ASN. It also means they don't have their own IP address space and could not build a transit network.

That's not true. Linode had numerous allocations, including up to a /16 (if I recall), before receiving an ASN. They simply announced them from datacenter transit, which has pros and cons.