Considering that Russia owns the islands and Japan gave up all claim to them, Taiwan and some other islands in 1951 ... I'd say Russia is just defending her territory.
was it disproportionate?
It would have worked in the past. However, things are not the same anymore. So-called 'northern islands' is another emotional issue politicians can tap on.
As far as I know, Soviet Union took them because it rings around the entrance to Sea of Okhotsk.