Maybe so. Now try 4 heavy people plus luggage in the car. Even if nothing breaks, you will soon see why, despite what you choose to believe in the face of massive evidence to the contrary, coil springs can not and do not work on a road-going Mini.
Which is exactly why Alec Issigonis rejected coil springs in favour of the superb rubber cone springs in the first place.
With coil springs on a road Mini the very best you could hope for is a suspension almost as good as with rubber cone springs, although it is unlikely to happen.
On a race car it is a different matter. It will only ever be driven with one person in it and a very high initial spring rate, whilst being very stiff, will improve initial turn-in on corners on totally smooth race tracks.
Of course, the very low sidewalls of the 13" tyres will simply make it worse still.
But then, there are those who want to make a profit from selling coil spring conversions, so they will argue to the contrary, but without any engineering logic.