Its actually a bit of both, in that it would hurt economic development, but European conquest would go ahead roughly on schedule. I'd advise reading the article "
Malaria and French Imperialism" which covers disease and French colonial conquest. To put it bluntly, the French were medically incompetent with the usage of quinine (promptly forgetting the success they had in Algeria in the 1830s in dealing with the disease), and they took huge casualties to disease when they sent white troops into Africa. But they were nevertheless able to conquer huge swathes of the continent, because the only people who suffered really horrifying casualties were the advance vanguards, who were very small and mostly consisted of native troops under French officers. If you take vast casualties among a few dozen men, well that sucks for them, but it is insignificant for your empire as a whole. The only time they suffered really big casualties were for operations like Madagascar where they sent in big drafts of unacclimated Metropolitan troops who promptly dropped like flies, and since there were a lot of them, their casualties were significant.
But once the French had actually conquered the territory, the casualty rates dropped quite a lot, because there was proper rest, food, sanitation, shade, native support, and they could recuperate from malaria even without having proper quinine treatment of it. The death rate was still high, but manageable.
I think the British did a better job of using quinine, but the point is the French showed that it is possible to colonize a tropical territory without quinine. However, I still assume it had some utility for keeping death rates lower among the settlers, so it will impede economic exploitation through a death rate which will be marginally higher in French territories and perhaps much higher in British ones. But the territories will be colonized anyway, so as far as colors on a map, there won't be much difference.