Nobody "wins." TPTB keep feeding in reinforcements - first on side, then the other, so that the game keeps going all four days. Yeah, it's fun, but it is in no way a "cannon" event.
A few points to clarify:
1: Even when the events were called the canon events and did, in some way, influence the storyline they did not last all four days. At first they were two day events and then were expanded to three days. They never were four days.
2: In that time frame reinforcements were, in fact, added in an almost perpetual wave like deployment. So canon events were very much reliant upon reinforcements. The current feature events do not utilize such reinforcement styles. They do use them, but nowhere near the extent that previous canon events used them.
3: With the shift to feature events from canon events there is most definitely a "winning" side. Daily objectives are in play and influence the score quite heavily. If your sole definition of winning is wiping every unit of the other side off the board then, yes, you are correct in that there isn't a winner.