Is there anyone past or present who explicitly says the opposite, that Emuna and Bitachon are rather two completely separate ideas?
See this translation of a talk of the Lubavitcher Rebbe about the difference between Emunah and Bitachon:
An excerpt from there about Bitachon:
Trust, by contrast, implies not only that a person believes that his sustenance comes from G‑d, but also that we rely on Him, with absolute certainty, to provide it.
An excerpt about Emunah (footnote 12):
A person’s emunah is not necessarily integrated and internalized to the point that it translates into actual practice. Instead, it can remain a mere outsider, a makkif. Thus, for example, it is possible that before breaking intoa house, a thief will cry out to G‑d, [Who forbids burglary,] and ask Him to prosper his efforts! (See Berachos 63a, as cited in Ein Yaakov.) Such a self-contradiction is not possible with regard to bitachon.
See 2nd page of this article, though, the whole article is worth reading. Excerpt:
What is the difference between emunah and bitachon? They both involve the belief that G-d alone brought into being all existence and that He single-handedly runs the world. However, bitochon, trusting Hashem with one’s life, only arises out of a deeply ingrained sense of emunah.
The Ramban (Kisvei Ramban, Sefer HaEmunah U’Bitachon, Ch. 1) explains: “Emunah is like a tree and bitachon is similar to the fruit. The fruit is a sign of the tree [that it exists]. However, the tree is not a sign of the fruit since there are trees that do not bear fruit. Yet, there is no fruit without a tree.”
I don't have access to Ramba"n, currently, to review his entire statement. But, it seems, that he explains them as separate concepts.
the first two gates of chovos halevavos have the theme of emuna.
the third has the theme of the duty of serving God
the fourth deals with bitachon, trusting in God like a slave trusts in his master for providing his needs.
so it seems they are separate themes, but not completely. it is a kind of build up.
you cannot have trust without faith, and likewise your trust is only as strong as your faith.
but you can have faith without trust. One can know and believe that God exists but still not trust that God is taking care of him, for that He must study God's system of hashgacha (providence) and be doing God's will, etc. as explained there.