Historically, that's exactly what the forms were. Both Iain Abernethy and Bill Burgar point out that in Okinawa at the turn of the century, individual kata were not considered to be `part' of the fighting system but the actual `style'. I'm not fond of quoting myself, seems a bit arrogant, but since I wrote something a while back that expresses exactly what I want to say on this topic, I hope the following passage isn't taken that way. In the original Okinawan setting where Matsumura, Itosu, Azato and other karate pioneers got their skills, the only way any techniques were transmitted was by the kata themselves. The kihon line drills through which virtually everyone in the West who learned MAs in the current era was taught—the bread and butter of dojo/dojang/studio teaching methods everywhere—were unknown. From all available accounts, including his own autobiography, Funakoshi's training for the first decade with Itosu consisted solely of practicing the Naihanchi kata set and working out their bunkai (even though Motobu didn't think much of Funakoshi's analysis and suspected that Itosu had withheld the most effective applications from him; but then again, Motobu seems to have loathed GF personally); where else would he have learned his techs from except Naihanchi?—that's all he had to work with! And as Abernethy notes, Motobu wrote in Okinawa Kenpo Karate-jutsu that `the Naihanchi, Passai, Chinto and Rohai styles are not left in China today and only remain in Okinawa as active martial arts'. That comment makes it pretty clear that these kata were not regarded as `parts' of a martial art, add-ons so to speak, but were thought of as complete stand-alone fighting systems on their own. In a way, `karate' originally corresonded to a general description (in much the same way that the generic term kung fu covers an enormous variety of specific CMAs regarded by their practitioners as quite different from each other) comprising the various kata, each of which was a style unto itself. And as Burgar points out in his book,
the fact is that before circa 1880 it was the norm for karateka to know a small number of kata. We also know that each master of karate was capable of defending himself. Therefore his one, two or three kata contained all of the knowledge that he would have needed to achieve that goal. This means that each kata (or small group of kata) was a `style' in its own right.'
(p. 29). Motobu also mentions in the same 1926 book that `a master usually only had one kata in his style'.
So it seems to me that kata, and forms in general, have to be seen as constituting fighting systems on their own; the question is, do karate kata constitute a
complete fighting system? And what makes a system
complete. I've seen it argued, over and over again, that there are no complete fighting systems (karate/TKD/TSD is weak on groundwork, aikido is weak on strikes, this or that style is hopeless at this or that fighting range...), but while I think that you need to
train against attacks designed to take you to the ground, or that use empty hand techs that your system doesn't, I don't think that every MA has to contain the whole kitchen sink to be complete. A complete system has to provide you with ways to deal with attacks and ranges even if that system doesn't use such attacks itself, or train you to stay in those ranges (as vs. giving you the goods to get out of those ranges and back to familiar territory, which a complete system definitely has to).
So with karate, Abernethy and other bunkai-jutsu practitioners have shown, in great detail, how you can use karate in the ground game—not to `win' in the ground game, but to get
off the ground that your untrained, but violent and dangerous attacker has taken you to, before he does. Abernethy's detailed book
Grappling for Strikers does exactly this, and there's an increasing literature on how traditional karate-based techs (including those of the karate-based KMAs) can help you keep the fight at the stand-up CQ range that karate was designed for.
So that's why I checked the top option in the poll choices...