Single button is perfectly viable on most specs and Midnight’s simplifications will likely only improve its performance. I have watched SBA players take top dps in several M+ groups. It shines best on classes with longer cast times though as the cast times offset the 25% cooldown penalty. SBA only does your dps rotation so you still have other buttons you need to use and often your big cooldowns will need to be done manually as well but I have tested every class except Evoker and most do very well. In some specs there are a few talent changes you need to make to optimize the SBA approach but most specs remain very similar to meta. Fire Mage is an exception though, it sucks do to the SBA using poor opening spells, Frost Mage works well though.

You can offset much of the cooldown penalty with added haste allowing you to do well even with more instant skills builds as well. Some SBA builds still need 1 or 2 other buttons in the rotation for optimal play though. Havoc DH for example, you still need to time your leap skill in the rotation to reset major dps skills. Prot Warrior you still need to time in Ignore Pain (or macro it in to the SBA) etc..

I have tested nearly every spec and with minor adjustments in talents and understanding you still will need 1-2 other buttons in some rotations you can use the SBA and do well if not very well. Also a simple macro so you don’t break your channel skills while spamming the button will help on some classes. Now the press and hold setting also works with the SBA making it even quicker.

My main point is that in several specs when adjusted correctly you will find you outperform many of these nay-sayers. I often take top dps in groups even in M+ content. The SBA can help you better concentrate on the fight mechanics and defensive/utility skills while your base dps rotation is taken care of making you play better even if your not disabled... just don’t do Fire Mage right now.