Base whispiness will always introduce small detached bits, set it to 0 or 0.1 highest if you don't want them.
High noise roughness values will also introduce/increase them, it's best to keep it around 1.5-1.6. Noise variation clumping can help with diminishing them but may introduce other effects, but in general it's very useful to get less regular patterns.
Keep in mind that using only one noise for density will probably not be enough to get a realistic shape, it may end up looking too regular with only one noise. Use another noise node as the main density noise's mask to introduce irregularities, or for 'Final density'.
To get a more defined look it's important to use a high enough number of voxels, otherwise the light cache is not detailed enough. A good rule of thumb is that a v3 cloud layer should have a minimum of 20 voxels in its Y dimension (voxel buffer resolution in the cloud layer's optimization tab). Especially important for thicker clouds.
Another default parameter that's slightly too low for defined clouds is 'Sun glow amount', I find it needs to be around 2.5 to 3, and you can play with 'Sun glow power' to introduce more contrast. But this is highly dependent on the angle of the sun so it needs to be adjusted sometimes.
Yet another one is 'Ray marching Quality' in the Quality tab, it's default value at 0.1 is way too low, use a minimum of 1 and go higher if your clouds render too noisy.
Then, for better definition of cloud shapes, you can of course increase 'Edge sharpness' while decreasing 'Cloud density' to maintain the general density.
But yes, it's definitely not easy to get photorealistic results, it takes a lot of time since values leading to more realism increase the render time, and a lot of trying... and quite some luck to get the right noise pattern. And you probably want to avoid the Easy Clouds presets, I never found them to produce realistic shapes and always use a generic cloud layer and go from there.
