We can start the clock even further back. It would have been sensible, after Sauron's defeat at the War of the Last Alliance, to take military measures so that his forces could not use Mordor as a base. Although the inner part of Mordor is hard to occupy for non-orcs, a system of perimeter fortresses and patrols could be established. This is actually what happened, but it failed; Gondor was led to withdraw due to other circumstances, and places like Minas Ithil fell under the enemy's control.
It might have been sensible, at this point, to counterattack. This is also what happened, but regrettably King Eärnur of Gondor did not return - the line of kings in the south was broken and Gondor was net worse off than before.
Knowing about the Ring, it might have been sensible to look for it. They actually did, and Saruman kept looking even after discouraging others.
If you are playing the long game, you might think to build up an immensely powerful military force over a period of centuries. The most obvious precursor is the mighty kingdom of Numenor, and that didn't go very well. Elrond would be skeptical, even aside from the fact that becoming the immortal shadow ruler of a warlike nation is really more of a Sauron move.
In summary, they have tried a lot of the most sensible ideas. But in the long term, the problem is that Sauron keeps coming back, and they can never sustain the military strength necessary to defeat his forces absolutely. In Elrond's lifetime, various kingdoms have risen and dwindled. As he says, "I have seen three ages in the West of the world, and many defeats, and many fruitless victories."
Thus, the strategic situation for the bulk of the Third Age is one where the goodies are essentially under siege, and occasionally have larger wars that are very costly but inconclusive. No war to date has stopped orcs from eventually reoccupying Gundabad, and Gondor has been in a long stalemate of trying to contain Mordor while lacking the strength to attack it properly. Rivendell may be idyllic internally, but it is still the Last Homely House, set in the midst of a wild landscape crawling with danger. The Shire is at peace, but only thanks to the continual efforts of the Rangers who hold back threats from the North.
So at the point the main narrative begins, the status quo is the assumption that the goodies are mainly trying to survive, and have never inflicted a military defeat on the enemy that lasted in the long run. Elrond is personally familiar with all of this, even if not all of his allies share the same view. For example, Galdor asks whether the Grey Havens could withstand Sauron indefinitely - it's not obvious to him that they can't. Boromir is more confident in Gondor's strength, but Elrond is bitterly aware that over enough centuries, it cannot be sustained. Given the waning strength of the Elves, and the fact that Sauron just keeps coming back, he fears that even a military victory would only mean that the next time Sauron returns, he will face less opposition, and so can grind out a win in the very long term. This is not a cause for panic, because it's a strategic question for the millennia, but it does shape Elrond's thinking.
One of the main things that Elrond and Gandalf are doing at the Council is to bring everyone else around to their point of view. The hobbits note that Gandalf, in particular, has been privately lobbying everyone else about the threat posed by Mordor. They have already been engaged in low-level warfare for centuries, but the situation has recently come to a head. Elrond and Gandalf are too experienced to panic, but they are making essentially the correct choices given the new strategic reality. The Ring has been found and Sauron knows it. They have the chance to inflict a final defeat on him. They are actively pursuing a decisive course of action, using what strength they have.
