I am going to say that you need fins, just not he ones you are using. I have been experimenting with fins for decades now, and have developed a design I call the "scoop fin." Basically, is is a flat-blade fin which has the interior cut out, and replaced by a flexible membrane which is tight on the foot side, but forms a semicircle at the far end of the blade (see my modified White Stag Fins in the photo). This modified fin leaves almost no splash on the surface, and is more efficient that other blade types.
Take your fin and cut out all the material except a one-inch interior U-shape to attach the flexible material to, and cut the flexible blade material so as to be tight at the toes, but firm that semi-circle at the end of the fin. Use the cut-out blade material to form strips to sandwich the flexible blade material between, and glue them together. I use Shoe-Goo for the glue. Then drill holes and use either screws or rivets to ensure that the material stayes in place.
You will have a lighter fin, which provides scoop action channeling the water towards the rear effectively on both the up and down stroke.
Here is some of my early work on these fins, from the 1980s:
This shows a diagram of how the flexible inner part of the fin, the "scoop" would increase the force against the water.
And here's a test I conducted in Alexander Springs State Park, Florida in the 1970s of this concept, showing the flow of water with the strings attached to the screws holding the flexible inner part of the fin together.
SeaRat