Solaris 7 was out for quite a while really ... a couple of years is not a short time ...
it was not a 'rush job' and it had many new features, which was why it was Solaris 7 not Solaris 2.7, it was a completely new release in it's own right.
Solaris 8 is far more bloatware than Solaris 7, it takes up a lot more disk space. on a machine with a small disk, you could afford to lose some functionality for a much smaller product, since it is not a significant loss of functionality.
there are reasons for choosing either.
if you're on a fast machine with lots of disk space then, yes, go for Solaris 8 ...
if you need the functionality or you're on a slower machine with smaller disks then customise the Solaris 8 installation to fit.
if you don't need the functionality go for solaris 7.