>That's why the won the war in the first place.
Not really. The japanese ships were, iirc, mostly built in britain and germany. Plus, the chinese had many more ships. I've read that corruption and morale were important factors, but I don't think relative levels of industrialization mattered that much. Bear in mind, Japan did not build things like engines domestically until the 20th century.
Further, the indemnity was nearly four times the annual national budget, and paid in pound sterling. That's more than a 'few years'. That's absolutely transformative. Not to mention the capture of chinese naval vessels, territorial concessions, etc.
> Most exports of industrial goods went to other developed countries.
Depends on the era. The basic point I'm making is that early industrialization, i.e. the wool trade, then the cotton trade, were generally export-driven, and export-driven to west africa. The cotton industry was also underwritten by colonialism insofar as it was predicated on slavery.
Pointing to countries that did not have direct roles in colonialism (although a surprising number of countries you wouldn't think of actually did - i.e. demmark in the slave trade) ignores the fact that colonialism basically amounted to a massive and sustained cash infusion into western europe. The spanish conquests of the new world, for example, brought so much gold and silver into europe they crashed the spanish economy, but I think it's obvious that this gold would have quickly escaped national borders and funded colonial and industrial ventures across western europe.