Hmmm no, I'm not your opinion on that. I already built multi-platform software, apps and frameworks which cross compile for iOs, Android and Windows. Multi platform support is always an overhead of course but if you're doing it right from the beginning it is in most cases a matter of good organization. Just my opinion and experience with developing for those platforms.
I'm no expert - nor am I a developer - so I'll always defer to experience. Mine is 'booksmart' (and that's being exceedingly kind).
At the same time - you can find multiple sources citing the difficulties of developing for iOS an Android. "Doing it right from the beginning" is the operative word.