Are the C-C bond lengths different in 2-methyl propene
The cases of benzene and 2-methyl propene are different.

In benzene, all carbon atoms are equivalent. One can also imagine the electron resonance.

In case of $\ce{CH3-C(CH3)=CH2}$ , the electrons have no place to move to create a delocalization cloud.

Additionally,  it would have to switch a hydrogen atoms between 3 atoms,
or create highly unstable $\ce{C=CH3}$

Such molecule would be highly reactive.