What makes you think the Bard's spells will be generic? If they follow the example of the Paladin and Ranger in the playtest, they'll write new spells just for the Bard, which will probably be analogous to older editions' bardic abilities.
Yes, they'll write a couple new spells at each level, but they'll also give the bard access to generic spells. So the end result is the bard is mostly just another spellcaster, mostly defined by their choice of spells. If a bard doesn't take spells unique to the bard they're very similar to every other caster. And defining classes by spells just means making more spells in a game that already has a f-tonne of spells just adds bloat.
I also tend to find many new spells forgettable. Spells that have been in that game twenty or thirty or even forty years tend to have survived because they're iconic and evocative. The names are descriptive, telling you what the spell does. Newer spells don't always do that well.
It's also a little too close to the 4e design of defining characters by their powers. Which I find bland and samey. I'd rather more unique non-spell abilities, so the bard feels like a bard and not just a wizard with a bard subclass.
There's so many other ways of making the bard different rather than just resorting to spells as the defining feature. This feels... lazy. Like they couldn't make another idea work in time or procrastinated on the bard too long and now have to just compromise by making it a dedicated spellcaster rather than a hybrid class.
I wonder if balance concerns are part of the reason. If they're having trouble making the bard balanced with the rogue and wizard while being a mix of both, making it a full spellcaster simplifies things; they can just balance it against the wizard and cleric, which they already have a good idea of power level compared to the martial classes.
Really, too many classes in D&D5 cast spells. I'm not a fan of rangers and paladins casting spells, let alone at the low levels they do in D&D Next. It makes a low magic campaign harder when only three classes don't have access to magical powers on a regular basis.
