No one wants them better than Avatars, I don't think. They just want them to be practical in their use.. In all my days, I have never used an Spirits to "get something off of me" like you mention - it simply doesn't work that way. Just summoning one generates sizable hate, which is bad enough, but Spirits are also prone to not reacting the way you want them to, sometimes doing the complete opposite thing you need of them. They also aren't particularly good tanks either, so I'm not sure where you're getting this from. The extremely high perp costs also makes it so that in a real emergency, where you're probably low on MP.. you're going to likely lose the spirit remarkably fast. At the absolute most, it can be used as a distraction for a couple of seconds so you can run away, which is a complete and utter disgrace if you consider that as the only thing they should ever be good for.
Likewise, we didn't always have siphon, so I again don't know what these things were meant to be good for prior to that skill being implemented.. The spirits seem wholly worthless in every other regard than using Siphon.
I don't see why we don't deserve both, really. SMN is such a ridiculously high MP costing job, and we really don't do much of anything that everyone else can't already do (and better). We at least had some advantages with buffs for awhile, but SCH pretty much replaced us entirely in that regard when they were introduced. We can potentially deal some good damage, but it seems unreliable compared to every other job just how much damage we're doing. And besides being tied down by our exorbitantly high MP costs (outside of Abyssea, anyway.. this doesn't matter to anyone in Abyssea anymore) we're also crippled to what we can do by our recast timers..
SMN as a whole never seemed as though it was designed especially well, they had interesting ideas for it but it never panned out in such a way that made it extremely useful. It was nice when we got auras awhile back so that we could refresh a whole party or what not, but the fact those auras crippled the Avatar's usability and promoted doing nothing so that you'd get the most out of the buff is just an insult if you ask me, really.