orbit - Rotational speeds of the material forming planets should increase, not decrease

You need to consider which material the planets are formed of.

Terrestrial planets are formed from less material (way less), and with less momentum (since they were orbiting near from the Sun). Gaseous planets (which is another name for external planets, due to their material), also known as gaseous giants, are formed with a lot more of material with a lot more of angular momentum.

Angular momentum formula is $vec L=vec rtimes mvec v$.

Orbital speed formula is $vec v=vecomegatimesvec r$.

Thus: $vec L=vec rtimes mvecomegatimesvec r$

Since all vectors are perpendicular:

$L=r^2 m omega$

Thus a higher mass $m$ makes a higher momentum $L$, and a higher distance to the Sun $r$ makes a quadratically higher momentum $L$.