The keyword here is ‘all’. There are some things optical computing is bad at. However there are some things it is unparalleled at. For example, light can multiplex. It can have much lower energy losses. It can run at much higher frequencies. It is by far the best way to transmit information at extremely high data rates. Even within a chip, free space optical communication has massive theoretical potential.

Your comment would have been an excellent one without the last sentence.

As a layperson I found this episode with Jeffrey Shainline an interesting discussion tangential to the topic of optoelectronic computing. The basic gist was that photons are good for communication, electrons are good for compute.

https://youtu.be/EwueqdgIvq4

You can just choose to use light at a smaller wavelength.

Also, less density by itself doesn't mean less performance, the larger optical components can just run faster to end up with higher overal performance.

Also path delay is not an issue if you have a task that can be pipelined for raw through put. Latency is less of issue in such scenarios.

So claiming there is no use for such things seems a stretch. It certainly can have niche uses. Bigger problem with a lot these papers is their tech needs to be at least reasonable to manufacture to have niche uses.

QC is also not going to replace general purpose electronic computers but augment them for certain classes of problems.

It doesn't need this density to be useful or better than electronics in many cases. For instance, photonic quantum computation happens at room temperature, but this doesn't seem like it will be feasible with any other method for long time, if ever.

Light has many inherent advantages over electricity for multiplexing/demultiplexing. Also, optical amplification works quite well too, and people use it on every long distance data cable nowadays.