I've been in the position of authoring a commercial SDK before and faced the same question. I do think Kotlin/Native is currently lacking both size & performance optimisations which will be widening the discrepancy between your iOS and Android library sizes.
With that said: iOS vs Android library size is ultimately a false comparison - they are different platforms that work differently and I always did find the iOS sizes to be generally larger.
Factors to consider are the degree to which SDK code is either linked into (included) or linked against (referenced), or the typical inclusion of multiple architecture 'slices' in the iOS binary.