Alpha-decay widths of SU3, deformed oscillator and cluster model wave functions are calculated quantitatively for the ground band levels of 8Be and the first K=0- band levels of 20Ne. Tails of the reduced width amplitudes of these model wave functions are amended by two methods, of which one is to connect smoothly the inner original reduced width amplitude with the resonance tail given by the release energy of α particle, and the other is to apply the Green's-function method developed by Kawai and Yazaki for the calculation of the radial form factor for the stripping or pick up reactions. From comparisons of the calculated results with experiments it is concluded that the SU3 model is insufficient to reproduce large α-decay widths. It is further shown that the deformed oscillator model is also considered to be inappropriate for the general explanation of the (rotational) levels with large cluster widths. From these consequences on SU3 and deformed oscillator models and by the numerical confirmation that the cluster model wave functions can naturally reproduce the experiments consistently with the variational energy calculations, the importance of the molecular viewpoint in light nuclei is emphasized.