I think there is a tendency to underestimate the importance of story to class concept. The concept of a druid, cemented after decades not just in D&D but in other media such as World of Warcraft and so on, is of a spell caster empowered by their link to the natural world, which allows them to shape shift into beast from the natural world. Specific animals. I think what a lot of advocates for templates are resisting is the fact that a lot of folks demonstrably do not want a la carte templates. That is not what the druid is, conceptually, to many people, and I don't think trying to force the template option is not going to change their minds. It's not changing mine.
Which I guess is a very heart of the matter issue: what CAN a druid turn into?
Look at the list I posted above as the PHB list. For sake of argument, let's assume that is the only choices that a druid can select from. What's missing? Well, lots of things. Dogs, squirrels, cows, coyotes, elephants, monkeys, bass, bees, doves, prihanna, etc. That is a wide range of options I can find in the real world that a druid cannot turn into, and that is without bringing in megafauna or dinosaurs, let alone fantastic beasts. Are we suggesting that those are the only things a druid's magic will allow? It's a bold world building assumption! Maybe the primal spirits of tigers will lend a druid their form, but the primal spirits of cows will not! Of course, the limited list doesn't account for any sort of environmental difference (with arctic druids turning into crocodiles but not polar bears) and the weight of the list is on weaker forms (none are above CR 1) both are only solved by expanding the list exponentially. (Again, at the cost of page space and comparison time).
Which brings me back to the Crux of the problem: if a druid wants to turn into an animal that isn't in the back of the PHB (like a duck), what is the answer? It's either: 1.) No, there is no stat block therefore you cannot choose that form, 2. Yes, but pick another stat block and call it something else, or 3. Pick this generic template and call it whatever you want. Two of those options are still effectively "pick stats and call it something else" one just involves extra steps.