Yes, the self-employed in the UK contribute less because they receive less benefits - same as here. Nor do they require the same benefits - by definition they cannot become unemployed.
Personally, I would prefer the German system where the self-employed generally fall outside the social security system completely. However, if the self-employed are to be kept within the social security system, then the position in the UK looks reasonably balanced to me in terms of aligning contributions and benefits.