The main thing I see here is that usually, if you can kill all of your opponents' units, you'll win by default anyway.
Using Warhammer 40,000 as an example. In 5th edition, there were 3 possible missions you might have to fight - "capture enemy base", "king of the hill", and "destroy everything". The problem was that all of the missions had "if enemy has no units left on the field, you automatically win" as a victory condition, and lists built around sheer killing power tended to be able to compete in all situations by virtually ignoring the objective and parking a single cheap unit on it at the end.
So it is with battletech. If I have to capture a specific building for information inside it and you have mechs defending it, the simplest solution is to destroy all the defenders, then take my sweet time finding that information and leaving with it without any external pressure. It doesn't matter how slow my force is, as long as we eventually beat our opponents into the dirt and have a single mobile mech at the end, we still win.
There are missions that avert this by having you chase precious cargo, but you're generally best not using mechs for that anyway - airborne units are all generally faster than ground sloggers, and a VTOL with a platoon or two of troops can usually capture a lightly defended unit on its own.
Simple, I have techs in the building, and they are deleting the database. If it takes too long for you to get there, then you lose, even if you kill the defenders.
Most of the games I play are carefully set up to keep "just default to killing everyone" from being an easy default option..... In addition, forced withdrawal helps a lot with it.
I had one game, where the objective on one side was to retake a prison camp --- it was set in an area of city, and the base had already been attacked, and the defenders driven off --- the attackers were now evacuating the prisoners, making them the defenders for the scenario.... the new attacking player, tasked with recapturing the base, chose mostly heavy and assault mechs, and came in with the attitude that he was going to kill all the defenders, and win by default.... what he didn't count on was one lance buying time, while the rest formed up on the evacuating armored cars, and just ran off the field.... he did manage to kill 3 mechs, and recaptured an empty building..... but, he lost the scenario. Had he used fast mechs, he could have forced a firefight, which would have resulted in the evacuees not leaving the building.... they were loaded in standard military trucks, and could not risk driving out with nothing but canvas guarding their people.
However, the big mechs never got in range of the trucks....
Capturing a dropship before it lifts off... etc.... are pretty much the way most scenarios I create are built. We usually have a victory point system, and there are points for killing opposing forces, but we usually set it up, so that the best you can get is a marginal victory, at best, that way...... and as soon as one side is done, we call the game, and decide victory right there. Any objectives not completed, are not completed. Of course, this has also once resulted in a military officer managing to hook up with friendly infantry, at which point, they commandeered a vehicle, and proceeded to drive the school bus they hijacked across 3 maps and off the board.....
Since this is a military game, there should be some form of military objective, and if that objective is to destroy as many units as possible, then there should be some form of victory for preserving your command, as in, inflicting damage, and then retreating units off --- if I can get some mission kills of your mechs, and still get all of mine off my end of the board, that it still a partial victory for me... you might have that plot of dirt, but I can repair my forces for later......it isn't always about owning dirt.
Now, if the mission is to take or hold a strategic terrain feature, we are talking a different story. However, I still don't necessarily have to kill you, just push you back enough, that you can't take that hill .....
Nahuris