I’m from a country that follows the UK A-levels system. Although majority of my school ends up with outstanding A levels, most are like you, in that they do not score well in internal exams (not so much because of laziness, but usually because the internal exams are harder than the A levels). Even so, because of the sheer difficulty of competing as an international against so many brilliant peers, few (if any at all) applicants have been accepted to a top tier school without consistently good internal results.
When they look at poor internal results, depending on the context of the school, they come up with two conclusions - either you’re slacking and not truly dedicated/interested in learning, or you are struggling with a rigorous curriculum, and they’re more likely to admit someone who could manage the difficult curriculum.