I strongly disagree with the bolded parts.
First off I'd say "most" paly tanks go for 15% exp 2nd even if most just went for 7.5% that by itself isn't enough reason to do it.
Exp hard cap is one of the
most important things to aim for if you plan on doing any kind of progress raiding, once bosses are on farm sure go for 7.5% and more haste, but there's just far too many boss abilities that you need to have SotR up for to risk getting parried at a bad time.
I'll just leave this
link here as Sloot and Thels say it much better than I can.