This is about this question:
I'll concede that the title is somewhat broad. But I did my best to suggest objective, factual methods of answering it that can follow formulas actually in use.
Suggestion 1: How many "extra" men were there on the gunboats that were assisting Grant, but technically not under his direct command?
This is a matter of record, except that I don't have access to these records.
Suggestion 2: Instead of comparing "men," compare the firepower of the guns on the gunboats versus that of Grant's 24,000 infantry.
Someone at West Point or Annapolis would probably know the answer to this question.
Suggestion 3: Estimate the value of artillery as a force multiplier. This is a bit more subjective than the first two, but war game makers do this from time to time. That is, they create rules like:
"Artillery increases the attackers' odds from one to one to two to one. Air power increases them to four to one."
While these are necessarily "guesstimates," they are grounded in historical records. At the highest level, the Pentagon has powerful simulators for war games.
Suggestion 4 was just a "catchall" so I won't discuss it further.
And the question was not "What are the true odds…" (an opinion) but "How do people guesstimate the "true" odds…?" (factual).
The people mentioned above who are tasked with making these guesstimates could all give you factual, objective answers about what they do.
So why would my question be considered opinion based?