ELI5 What is wrong with SMN?

[RyuujinZERO]

I recently picked up SMN having not played it since ARR; I wasn't much of a fan of it back then and ignored it during HW.

I've been enjoying the mechanics quite a lot, and it's damage seems respectable compared to PUGs of other classes and my previous DPS alt-class (MCH). The only mechanical issue of note that seemed to stand out to me was a lack of spammable hard AoE skills, particularly once the time-to-kill on a target drops below 15 seconds, they don't really have any good options besides spamming Ruin (Weaving in AoE's like painflare not withstanding). But if you're only 15 seconds from finishing the trash pull, then the trash pull is almost over anyway and shaving off a few seconds more doesn't change much.

But every time I hear SMN discussed all I'm hearing is 'ded class'. What exactly am I missing?