It is only because we do not have a framework of analysis & measurement that some think memes are a metaphor...
Memes are not metaphors. Are genes metaphors?
Were genes metaphors before we had concrete evidence of the DNA molecule?
Memes are replicators. Like genes, they follow trajectories (which can be mathematically modeled) of adaptation and replication.
They accumulate information & complexity. They alter their environment.
If you can't suspend a conviction that memetics is simply a metaphor about human culture, you are in good company. But take a little time to indulge the possibility memetics could be much more.
To say memes are exactly like phage (viruses) or bacteria is wrong. Phage and bacteria are products of genes.
Memeplexes are unique replicators. Their outcomes, their artifacts, are unique to memes. As such, they deserve their own examination.