Yes but no but
This is 50% right, as I have come to understand it. Yes, SQL is crap at expressing these things as it has no explicit looping, and works in sets, not linear chains. There are kludges to fix this of course via stored procedures, and stored tables, and nasty operators (CONNECT anyone?) but it isn't pretty. Impedance mismatch, yes.
It is, however, pretty easy to encode them in relational databases (e.g. two tables, one of nodes, and one of edges). Directions are also easy to express.
So the problem here is one of semantic power, and that is something that is easily added, so I think graph extensions to SQL will appear, and performance will be equivalent if not better, as soon as someone can be bothered to add it to mariaDB. Like all good ideas, it has probably already happened.