Okay I see the problem.
The recipe is what it should be: flour, butter, and sugar are all equal to the weight of the eggs in the shell. The Victoria sponge is a misnomer since the cake is actually a pound cake. This distinction is important because cake is baked to internal temperature. But more on that below.
The dry cake is a result of oven temperature and the baking tin.
The cake batter in direct contact with the metal will always bake faster than the batter in the center of the cake.
Dark colored metal, coated metal, and anodized aluminum conduct heat much more intensely than a natural metal. This results in even faster baking of the cake batter in direct contact with the metal.
By the time the center is baked the crust on the sides and bottom of the cake is thick and tough. And the entire cake through and through is dry.
The picture below demonstrates the effect of bakeware material on cake. These chiffon cakes were baked using the same recipe, the same batter, mixed at the same time, baked at the same time; so same oven temperature, and baked for the same amount of time. The only difference was the top cake was baked in an anodized aluminum pan, and the bottom cake was baked in a natural metal pan.
As you can see there is a marked difference in the look of the baked cakes. The dark crust on the top cake is dry, tough, and aesthetically unpleasing. The entire cake is significantly drier than the light colored cake with no crust on the bottom. And the bottom cake came out of the tin with no crust on the side and bottom.
The second photo shows another orange chiffon cake. Note there is no dark crust around the side of either cake. It literally comes out of the pan that way. The top of the cake has a brown crust because it is fully exposed to the dry heat in the oven. The second cake in the background has the top crust removed. I always remove the top crust of my cakes for better aesthetics when The cake is sliced and plated.
All dark metal, nonstick coating, and anodized aluminum cake tins overbake because they conduct heat much more intensely than a natural metal tin.
When using a dark colored metal, coated metal, or anodized aluminum you must reduce the baking temperature. When using celsius if the recipe states an oven temperature of 170°C, reduce the temperature up to 160°C.
160°C is comparable to 325°F.
I use natural metal pans and bake all of my cakes are baked at 325°F (162°C).
THE PRICE OF THE TIN IS NOT AN INDICATOR OF QUALITY. It’s about the type of metal and the coating. The tins I use are cheaper than most tins. And most commercial kitchens use this type of bakeware as it conducts heat less Intensely.
Most of the bakeware sold in the UK Is dark metal and coated. If you decide to invest in new cake tins, I would recommend PME or Lakeland’s Mary Berry cake tin. And specifically the Mary Barry because all of Lakeland other tins are dark and coated. With the PME and Mary Berry tins the oven temperature WILL STILL need to be reduced. But they should produce a slightly better result.
Baking a cake to internal temperature rather than time is also very important. As batter bakes, the water in the ingredients evaporates.
Victoria sponge does not have any added liquid. It gets all of its moisture from eggs and butter. Substituting margarine for butter may reduce the amount of water in the batter as the amount of water in margarine varies by manufacturer.
But all baked goods regardless of the type, should be baked to internal temperature, not time.
Butter cakes (includes pound cake) center of cake internal temperature of 200°F - 205°F is done.
Foam, angel food, sponge cakes: 205°F - 210°F is done.
Water boils at 212°F. Never allow a cake to go over 212°F as the amount of loss hydration due to evaporation will result.
As I mentioned above the Victoria sponge is not a sponge, it is a pound cake. Bake it to the internal temperature of a pound cake.
Mixing is also very important. One of the most common mistakes made in baking is improperly cream in the butter (or margarine) and sugar. Below is a link explaining how creaming is properly done. This applies to all creaming of butter and sugar regardless if it is for cookies or cake.
Since the Victoria sandwich is not iced it will dry out more quickly than an iced cake. Since you use a whipped cream filling this cake must be refrigerated. And refrigeration dries out cake. There’s no full proof way to keep this moist.
To store the cake wrap it in two layers of plastic wrap. If you have a cake carrier, place the wrapped cake in it. Let the cake warm up on the counter before serving. Then sprinkle on the powdered or caster sugar.
When storing a cake that has been sliced already, please a piece of plastic film directly on The surface of the cut area. Then wrap the cake in plastic as described above.
Placing a piece of plastic directly on the surface of the cut area applies to an iced cake as well. Of course with an iced cake you cannot wrap the entire cake in plastic. But you should cover the sliced section.
How to cream butter
https://www.seriouseats.com/2015/12/cookie-science-creaming-butter-sugar.html
The only difference in these two cakes is the type of tin. I sliced the top cake open to show the interior—The interior is darker than the cake baked in a natural metal cake tin
Cake in the forefront is what the cake looks like out of the pan. There is no dry, dark crust on the sides and the bottom. The cake in the back ground has the top crust remove.
The reason I remove the top crust is for aesthetics. This is a test cake for a birthday cake If you zoom in you will see there is no dark crust line between the cake and the buttercream. How a slice of cake looks plated is part of the decorating process. I do not like to see brown crust lines any where on my cakes.
I've come to realise, from various baking videos, how important it is to gently fold in flour and not push out the air, because my sponge is super light and airy. So I used my new stand mixer for the butter, sugar and eggs and then did the flour by hand. By the way, the first thing that hit me on flavour was the butteriness and then I remembered that I didn't use butter, I used Stork margarine. In fact, I used a copy of Stork, Tesco's own baking spread. Honestly it's so much cheaper to buy a 500g tub of spread than a 250g block of butter, and it's every bit as good for cakes. 
