Shield Swipe needs to be more useful (aka, part of the the standard threat rotation) and PLD would feel a bit more engaging since you'd have to watch for it and react, as the window to use it isn't all that long. Might change the preference between Tower/Kite/Buckler, but not like there's a ton of all three of those at every level range to pick and choose from at the moment.

Some people like a class that just works. The fight itself can provide the engagement. Rather than spending most of their time having to focus on class mechanics they can instead focus on the fight (and how it differs from other fights). Good to have options.

There are those that love Summoner for all the micro managing you have to do to play optimally. Others will hate it for the same reason.