je možné použít tento idiom bez off uprostřed?
No. You can „come second“ in a race or competition or in some kind of
rating or scoring context, but when you add „best“, you need
„come off“.
It's important ro realise that „come off“, which can have many meanings,
is functioning as a phrasal verb in this meaning, so [come
off], and not [come] [+ preposition].
Nicméně britské média a někteří mluvčí tuto frázi používají
právě bez použití onoho off.
I wouldn't expect to see that in this specific idiomatic sense of „come
off“ (which has many different meanings). If you can quote an example and link
to the context, I can try to provide an explanation.