That sounds like circular evidence.
There are problems if we take Hades as a place.
The first problem - Jesus was
dead. He gave up the (Holy) ghost, His body was pierced, and His soul died because He became sin for us. So triple dead, body, soul and spirit. Now, which part of Jesus was then preaching in Hades?
To make this worse, Jesus is the Word of God.
So if Word of God was
dead in Sheol, who communicated the message?
The Bible teaches that the dead see not, hear not, speak not, have no knowledge, know nothing, and so forth...
(This brings up another problem, how would the listeners hear when they are dead and "know
nothing", and seems to seriously discourage taking this so literally, and rather talks about the
spiritually dead)
If we have to challenge basic premises of the Bible such as Jesus being
really dead during those 3 days, or ask ourselves questions such as "How dead is
dead?", taking Sheol as a place calls for rethinking.
I could continue, but let's focus on this for now.
Regarding the reference in Jonah foreshadowing Jesus being buried:
There is
no Scriptural evidence to confirm that "the heart of the earth" is a specific location.
But there is multiple Bible evidence which suggests that this is a figure of speech:
"heart of the seas" in Jonah 2:3, also "heart of the heavens"/"midst of heaven" in Deut 4:11
Matthew Poole's Commentary
...and the midst or the heart of it is not only that which is strictly and properly the middle part, but that which is within it, though but a little way, in which sense places or persons or things are said to be in the heart of the sea, Exodus 15:8 Proverbs 23:34 Ezekiel 28:2; and Christ in the heart of the earth, Matthew 12:40.
It is reasonable to take this a poetic way to say "underground", which would be apt as Jesus was enclosed in a cave.
As to, what was Jesus doing there then? Well, I think it was not a location, but a
state of being dead, imo, which clears up the said problems. There was also the location of the literal cave for the body, so Jonah's foreshadowing isn't contradicted. I've wrote in post #116 that preaching is not directly tied to Jesus being in the grave (people add to this verse what is not there because they take Sheol as some spiritual dimension place), and about when did actually Jesus preach, at least what I believe so far.