inorganic chemistry - If d-electrons are such poor shielders, why do trends increase more gradually across the d-block than the s or p-block?

If I understand correctly, the shielding effect of d- (and f-) electrons seems to be much poorer than those of s- and p-electrons, due to the fact that they are less penetrating, have less electron density near the nucleus and so on (as can be seen from radial distribution functions).

However, trends for ionization energy, electron affinity, and electronegativity are MUCH more gradual than for s and p-blocks. This means that the effective nuclear charge ALSO increases much more gradually in the d-block, as confirmed by Slater and Clementi values. If d-electrons were poor shielders, surely this would mean that Z-eff would be much higher?

Doesn't this mean that, say for period 4, 3d-electrons are much more effective at shielding the 4s-electrons, than the 4s-electrons are at shielding 4p-electrons? Why does this happen?

Is there another factor at play? Is it because we are adding electrons to an "inner shell" that the shielding becomes more effective? Is Z-eff = Z - S an incorrect guideline to use?