To be honest, this topic kind of brings me back to wanting a somewhat limited pool from which to draw all class's development (in other words, some exclusivity). I want pet-raising to be huge. Absolutely huge. But I don't like the idea that you'd require a whip or the like just to work with said pet. It doesn't seem like an armory type decision at all. Nor does it really seem like a "job" decision as jobs have been dived thus far throughout the series (essentially classes, rather than pursuits). [I personally see the ideal role of jobs as being a pursuit of some sort of personal preference in the way one fights (and more) that manifests itself in certain class choices that eventually develops into a very specific fitting "job" that probably isn't even preset.] I'd rather lose some sort of 'ingenious insight' that I'd otherwise have into some other art, be it swordplay or archery or black magic, in exchange for the experience of basically sharing the entirety of my pursuits with this pet. No matter what particular class I'm in, I could still work with my pet; he's a relationship and a share of my combat mechanic and combat power (not necessarily an augmentation, just a diversifying share) first and foremost. He is not a familiar. He does not vanish into another plane as soon as I'm not feeding him magic. He might well complain from lack of food though.
Like in leveling with a path companion (in the way I would hope to be possible), Chocobo, etc, one's time, the building of the relationship, and perhaps even "keys" (notably levels and likely pet-type-unique quests) will probably come into account. If I were staying as a beastmaster (kind of like the choice of equipping a job stone as opposed to having the open class version) consistently, I'd be seeing the pets I leveled with all the time--they're my primary or co-primary tool of combat after all. But, let's say I didn't want to divide my learning up at all, or wanted to focus on something else. Depending the way xp works (yes, we are solidly grounded in ambiguous theory now, not just the way ARR currently works and likely will continue working), that pet may be progressing, akin to a dynamic NPC, as you do, and you'd still be seeing it at learning from it at different points in time before restarting your partnership. Or, perhaps that could be the case only for key beast NPCs, which would truly function like your path companions, but with an additional level of control for Beastmasters. [Mage classes for instance would have additional things to enjoy from quests involving spirits or repeating spirit characters, and physical classes to their respective weapons, such as in 'In Pursuit of the Dark Sword' type quests.] Well, that's ranty enough. I'll stop there.
Speaking of Puppet-masters... I'd love to be able to take a cursed weapon from one boss, the head from a Halloween special scarecrow boss, a mechanical carapace I dug up from an archaeological site in deep Thanalan, and a still-beating etherial heart from a Black Shroud outskirts questline, and from all that and my own crafting expertise have my perfect puppet. It's hard to beat Puppeteer in terms of carrying your leveling experience with you. As long as the puppets' building process is open to upgrades and adaptation, it's a perfect sink for one's own collection, perfectionism, and resourcefulness alike.
Tldr; I want huge adaptability with great investment (in terms of choices and experiences, not just as a time sink) for every class, but pet classes are where it should be most noticeable and key to the class experience [as opposed to skill and theory or "know your class, know thyself", pet classes should be more "know your partner, know yourself"]. However, I don't know how well it will do as a stand-alone class and especially how well it will do within the armory system. Personally, I'd prefer them as something of a job augmentation onto another class, almost like a Swordsman-Beastmaster. This would allow greater and more reasonable versatility in how one works with their pet. [I'd actually would have liked to see summoner as a augmentation onto Conjurer, Thaumaturge, and Arcanist separately, each with different pet types and priorities befitting their respective elemental-spiritual, dark-ritualistic, and theoretical-magic ties.]
To me "Tamer" seems like a Disciple of Land class, with skinning and herding being sub-components of that class. It does not seem combat-capable until having already reached the title of Beast Master. Its strength should then lie in its adaptability and diversification of earlier class playstyles and complementation of their roles. After that, certain ties between pet and weapon types (without forcing pairing decisions) should be able to lead to advanced jobs.