Who has the upper hand is going to change constantly based on perk loadouts, maps, killer choice, mistakes made by either side, etc. They had the upper hand initially because a Trapper against a SWF is a hard game. SWF can call out where traps are and then disarm them for each other. There may have been times in the game where you had the upper hand, and they had to adjust their play style in order to get ahead again.

There just isn't a way that both sides will have a 50/50 chance of winning in every game. There are too many variables that will constantly change in the match. There are killers designed around the concept of variables changing. Oni has a snowball effect where he can be losing but the moment he gains the upper hand, he quickly starts taking back control. Nemesis can have games turned around by the work of his zombies.

There's a chance you demolish this exact group if you played this game again, or if you change one perk, or if you change your killer, etc. So much of the game is based on chance and random game elements. Skills and perks and killer choice are meant to try and skew those odds in your favor. Trapper is better against solo queue players, harder against swf. Circle of healing is a great perk that puts the odds in the survivors favor... unless the totem spawns are bad, or they're playing against plague, or one of their teammates keeps leading the killer to the boon. Etc.

Like I said you weren't punished, and it looks like you played well. But they won by a margin.