1. SMN as rare as COR? Haha, no. SMN has never, ever been as rare as COR; as I recall, COR has been the least-played job in the game since its release (yes, less played than PUP). The most recent Vana'diel Census that I've seen, 2009, shows twice as many SMNs as CORs.

2. Summoning magic skill under cap isn't very useful, true. Elemental Siphon and Avatar's Favor get relatively irrelevant boosts compared to the boosts to MAcc from Elemental or Enfeebling. However, I also do not believe that any other job gets the same kind increase over cap as SMN does; Ward durations can be more than doubled by stacking skill, while still increasing accuracy and damage of Rages.

3. No, SMN does not need melee gear. PUP was initially intended and conceptualized as a combination melee and pet job. Even since its first appearance in the series, Summoner has -never- been a melee job. Summoners have always been reliant on their summons, with no real melee capability.

4. Between rages, wards, favors, and ease of recast, I find avatars to be quite versatile. SMN is quite a strong solo job, especially with all of the perpetuation decreases and MP recovery granted to the job. No, it is not the strongest, but it is not the most useless job in the game. In addition, favors and wards allow SMN to be of use to a party also. I also don't see what you're talking about with ignoring the avatars with poor favors. Different avatars are used for different situations. I wouldn't summon Fenrir just for its favor, but it has other uses as well. Meanwhile, if I do need extra Refresh for myself or my party, I know I can pull out Diabolos and use his favor. This versatility is also why our buffs are not as strong or long-lasting as BRD's. BRD is defined by its songs; if a job with other capabilities (i.e. SMN) could match those, BRD would be a completely, utterly useless job. COR, also, is mostly defined by its buffs, which are also unreliable since their strength is determined by dice rolls. SMN buffs may be short, but they're fairly strong and the avatars can deal damage in addition to using buffs.

5. What other gear does SMN really need? Using proper gear, SMN can cap both perpetuation reduction and blood pact delay reduction with no trouble, while still having other slots to boost summoning magic skill or avatar MAB or whatever else you may need.

6. Minor point: DRG's Call Wyvern was it's 2-hour, an ability that's supposed to be incredibly strong; however, it was a pet that was important to DRG's utility and damage, in addition to dying easily and being difficult to heal. SMN does not have the same sort of issue; spirits do suck, but then again SMN doesn't need them to be a functional job, nor are they a 2-hour or equivalent ability that's supposed to be ridiculously strong. (For that matter, Astral Flow has been a useful 2-hour for as long as I've been playing; pre-cap increase it was a very common CoP mission strategy, and it's still the main ability enabling pretty much the fastest way to level jobs from 10-30.) They just aren't a necessary component to... pretty much anything SMN does. Not every spell that BLU or BLM or RDM gets is useful either; see, Deodorize. Does SMN have a higher proportion of less useful spells? Yes, very much so, but I'd rather have weak spirits than no spirits at all.

My conclusion: No, SMN is not the best job. Could it stand to be better? Yes, of course. However, SMN is able to deal good damage and utilize many full-party buffs with a rather high degree of personal safety, since the avatar is the one doing most of the work and can be quickly resummoned in the event that it is defeated. It is a strong job in its own ways.

EDIT: Didn't mean to make this post so long. Sorry for the wall o' text.