The DC-DC shown looks decent enough, what is
"unreliable" about it?
The ripple voltage seems a bit high for anything
"analog style".
There's "reliable" and there's "reliable". You can't
afford the HiRel parts I developed and you would
not need their resistance to abuse (which is why
they sell for as much as they do - nobody else
survives when da shizzle gets rizzle).
A commercial linear regulator or high power op
amp would probably do what you want. Depending
on how fat the FET. Any major brand linear IC is
going to be pretty reliable -if you respect the
datasheet application limits- and no IC can be
expected to be reliable if you go and violate them.
Look there, if you're blowing stuff up.