Sure, in an quantifiable way, Japanese investments and industrial development improved the economy of Korea.

But for a claim that Imperial Japanese occupation improved quality of life in Korea, we would have to include the effects of an oppressive government, literal treatment as second class citizens, labor exploitation, slave labor, forced conscription, coercion of women into prostitution, forced assimilation, repression of history and culture, banning of the native language, etc.

The vast majority of Koreans were not happy with Japanese occupation and even many of those who cooperated with the occupation administration did it out of practicality and had little love for the methods and policies of the colonial government.

As for Koreans were common in the military and perpetrators of POW crimes.

The vast majority of Koreans that were conscripted into the military were for labor purposes, most of them going to work in key strategic factories, construction, etc.

Those accepted into combat roles in the military were actually extremely few. In fact, they were incredibly selective of who was allowed to participate in the Imperial armed forces.

This policy only changed near the end of the war, when Japan was facing shortages of both veterans and fresh recruits. Korean recruits were often seen as 'inferior' to Japanese recruits and as such, were only recruited as a last resort during the most dire months of the war.

Thus, it's highly improbably that Korean military serving under the Imperial forces can be held accountable for the many warcrimes that were committed throughout the war.

And even when Korean conscription was in full swing, the vast majority of them were placed in support roles, theoretically to free up more capable Japanese men for the fighting. This meant that they were not very different from the laborers that had been forcibly recruited and moved to Japan, Manchuria, China, etc.

Many Japanese officers did not see the Korean recruits as a credit to their military strength. In fact, some did not even see them as allies and would not trust them with weapons.

That being said, there are Korean members of the Imperial forces who did in fact commit war crimes.

But this has to be put in perspective since often, when the Korean war criminals are brought up in conversation, it is a thinly veiled attempt to 'spread' the blame or even to entirely shift the blame and claim that most Japanese soldiers were innocent.

In such touchy topics, it's incredibly important to not color the facts as much as possible. For example, how would one quantify which warcrimes were 'worse' than other ones? This is already an incredibly contentious question without adding more controversy on top.

Hope this answers your questions!