Of course you can fix up what it does manually, but the people who
are capable of doing that are the people who can do the whole thing
manually, just about as quickly.
Adjustkernel was, when it once worked, long long ago, primarily best
for people who had no idea what a kernel config file ever looked like,
nor how to tell what hardware their system might have in it, let alone
how it attaches to busses. Those kind of people mostly don't build
kernels any more, they just run generic - but I talked to one a month or
so ago, who had been unfortunate enough to see the doc that says (something
like) "or you can use adjustkernel" and believed it, then couldn't understand
why the resulting kernel didn't link. I just told him not to bother...
(with adjustkernel, he needed to be able to config/build a new kernel.)
I had wondered for ages why it was still hanging around. Good riddance.
(Just remove it from the "how to build a kernel" doc as well, and get that
change pulled up to *all* earlier release branches that are still active.)