Has Full Metal Alchemist Brotherhood always been the number 1 top anime on MyAnimeList? I would like to know if there were animes which reigned supreme on MAL before and after FMAB made its entry on the list. Has any anime ever dethroned FMAB (even if temporarily) or has it always been the defending champion, to this date.

Thanks in Advance.
On this reddit thread, you can see state of top anime list since 2007 until 2016. According to it, FMA: Brotherhood was outscored by Gintama at least for some period of time.

This history thread is not up to date, but at least it answers your question - yes, there was another top anime since FMA:B was released.