The idea of themes and/or specialties being a preset list of abilities isn't a bad one in and of itself. Kits, PrCs, and Paths/Destinies are all short lists of preset, prepackaged abilities with a cool name that you choose to customize your character, and the devs mentioned a connection between themes and PrCs when mentioning that there might be "advanced themes" only accessible at higher levels. The problem is that in prior editions we've had those prepackaged advancement plus selectable advancement in the form of feats, and so far specialties and combat styles (schemes look pretty good so far) combine the locked-in advancement of PrCs/Paths with the lameness of many 3e/4e feats without providing the benefits of either (being a major defining feature and being modular, respectively). If specialties and combat styles had all the punch and pizazz of the stronger and more flavorful PrCs/Paths I doubt there would be as much resistance to their current inflexible form.

Having a preset progression for abilities can be good for newer or more casual players, which is why classes like the 3e barbarian and full-list casters classes are good to have: they provide all of their class features in one package, no pre-selection required, and allow for players to fiddle around with things in play without needing to build anything. The 3e fighter and sorcerer may have been intended as "beginner" classes (make anything you can imagine, just pick some feats or spells and go), but I'm sure we've all seen what can happen when new players make bad choices and get stuck with them, so obviously limiting options for newbies is a good idea...but we can also see, with the monk, swashbuckler, knight, and others, what happens when the devs try to provide entirely preset classes without having any idea what they're doing.

So, having said that, it seems to me that WotC screwed up when they decided to prepackage feats with the option of selecting them instead--they probably should have had some prepackaged and some selectable options to satisfy both camps. (They also shouldn't have yet again fallen into the traps of 3e's "you need the Improved Shoe Tying feat to double-knot your shoelaces" problem and 4e's "whee, another damage + status effect power" problem, but that's another issue entirely.) Given the weakness and lameness of current abilities, I'd be tempted to playtest treating combat styles and the weaker specialties as feats--that is, a fighter can take the Slayer "feat" or a character can take the Survivor "feat" and gain all benefits of the combat style/specialty in one level. That gives you the benefits of being able to say "I wanna be an archer fighter!" and have that mean something while also letting you have the fun of picking new abilities every time you gain a feat, and is reminiscent of the usual 3e houserule solution of collapsing weak feat trees into 1-2 feats to make them useful.