Is Finland Leaving Years of Educational Achievement on the Table?

Tim Shanahan argues that Finland's "illiterate kindergarteners" are not a useful exemplar for US schools, because Finnish children are much better off in general, health and welfare-wise, culturally homogenous, and because Finnish is particularly easy to learn to read (it is very phonetically straightforward, etc).

Those are all reasonable arguments, but it isn't clear why they don't serve equally well as arguments for starting reading and more academic instruction earlier in Finland. If Finnish is easy to read, the kids are well-fed and cared for by generally well-educated parents, shouldn't they be ready to get started in kindergarten?

On the other hand, if American five year olds are less well prepared for the more difficult intellectual task of reading English, isn't that a good argument for focusing kindergarten on more fundamental behavioral and social development, building a foundation of pre-literacy skills that will bring all children along reading in first and second grade?

If you believe Shanahan, you must also believe that Finland's already high literacy achievement could be even higher -- perhaps a whole "year of learning" higher -- if they would simply start their kids reading earlier. Obviously, we don't know what would happen, but I'm dubious.