The reason most likely why OP's FC removed them was because they invited OP under the hopes that they would become a potential Healing WHM for future Statics. However Yumi took it upon themselves to start gearing themselves to becoming a Tanky WHM without their consultation - forcing perhaps 7 other people to follow one person's ideas which is not ideal unless Yumi was the FC leader. (Which they weren't).
Further more, Yumi made a post about 10000 pages long without editing and double posting why he/she felt it was unreasonable to not have tanky healers then dismissing others opinions by saying theirs was the one true way.So yes, this would lead X to having problems with friends especially since Yumi's post slanders other healing WHMS. (Also joining DF as a Tanky healer and forcing it on X members? Yeah not so smart.)
Yumi's best decision here is to start his/her own FC and/or linkshell and make it a one that's designed on trying out certain fights. (There are people who like to mess around with mechanics and try new things so it's not hopeless.) FC name could be WHM Tanks R Us. /shrug