As an entirely separate note from the above:
4e roles and power sources were never straightjackets. Ever. Having a role in 4e just means, "This is what you're automatically good at." To lack a role would mean you were good at nothing inherently, and had to claw your way into being good at something, which...I sincerely hope I don't have to say why that would be bad. Even from PHB1, it was always possible to mix roles, and to take powers, feats, PPs, etc. that made you good at things outside your role. Some classes were hard to shape into certain roles, but it was rarely impossible to do--e.g., Paladins don't have a lot of Control effects, but multiclassing with a controller class and picking your powers wisely would let you grow in that direction, as could taking a useful PP.
Likewise, power sources weren't a straightjacket. They simply said what you definitely could draw on for power. Being a Wizard with Divine powers could be as easy as playing a half-elf, or multiclassing Cleric, or whatever. Choosing to mix your power sources was perfectly valid--some options even required it. And, as others have noted, this was perfectly supported by 4e Dark Sun, where the Divine power source doesn't exist, and the old 2e "elemental clerics" were an obvious, kludgy patch.
It is so infuriating to hear people still repeat--even a decade on--how "stifling" etc. 4e's roles and power sources were. They straight-up, flat-out were not. They gave you a floor to stand on, not a ceiling to hold you down. I will never understand why telling some people, "You're good at taking hits and holding an enemy's attention!" translates for them into "You are NEVER allowed to do ANYTHING but take hits and hold enemy attention! HOW DARE YOU EVEN ASK!!!!!" Nothing--not one thing--in roles or power sources says what you CANNOT do.
People made the accusations long before the Seeker existed, though, so I'm not sure how much it applies. I do totally agree that it fell really flat though! The Seeker, and the Binder Warlock, were both...reasonable ideas that manifested poorly.
It doesn't help, of course, that the Seeker was part of WotC's attempt to salvage the kinda-sorta terribly racist Ki power source, as was the Runepriest (originally a Ki Leader--it used ofuda rather than runes, more or less). I don't think we ever saw...whatever thing they intended as a Ki Defender. AKA, I kinda feel like the Seeker was doomed to fail regardless.
Also, the irony with the Seeker (and the Runepriest and Binder!) is that they weren't even grid-filling! Because those boxes on the grid already had something in them. Druid was already a (the?) Primal Controller, Cleric was the Divine Leader, Wizard was the Arcane Controller. They weren't empty checkboxes getting a perfunctory submission to ensure every box was checked. They were, instead, trying to over-load existing boxes with more things. And I totally agree that trying to wedge multiple classes into the same niche is difficult and not likely to work very well. If that were what was typically meant by "grid-filling," I'd have no problem with the term.
On Elemental vs Primal: yeah, Elemental was a bit like Shadow (except that Shadow did have one class to its name, the Assassin). That is, you had things like the Elementalist Sorcerer or the like, but no Elemental classes. The Primal Spirits were, more or less, the "emergent" magic of the material world itself, an unexpected bonus from the efforts that the Primordials (= Elemental power) and Deities (= Divine power) put into making it. Primal magic isn't so much "elemental" per se as it is animistic and holistic: it's not that you tap into the raw power of pure fire, but rather that you call upon the spirit of the First Flame for her guidance or power; it's not that you bring a rock-berg in from the Elemental Chaos, but that you channel Grandfather Mountain to weigh down on your foes as though he himself had fallen upon them. (The former is a Shaman's way of looking at it, while the latter is closer to a Warden's.)
