Link for additional Zacny Myth-ologising.
For me, it was always in the multiplayer. In campaign missions (and even skirmish modes to an extent) then you can set up a good fort defence (Starcraft 2 did it a few times - something everyone can currently play for free with that first campaign being totally free now) but it always felt a bit staged. It had elements of a puzzle, you could feel how the pieces were meant to move against each other. Someone had already done some planning and you were here to work out what a valid solution was. As soon as you put another person in control of the hordes, that all goes out the window.
We used to play a lot of LAN weekends. Doom & Descent over null-modem (that’s a serial cable being used as a dodgy network link for the younger/non-PC among you), through Quake/AQ2 & Total Annihilation over thin-net, into the more modern era of Unreal Tournament & Counter-Strike over what would still be recognisable today as a local network (hubs/switches and [not-actually]RJ45 point-to-point cables).
The dominant strategy game was Total Annihilation. Custom ini file slowly increasing the unit cap as our computers got faster, ever-expanding selection of units from not only expansions but free downloads of new units and balancing patches offered up online. It was the game to play for 2-3 hours as we slowly ground out a victory and watched to find out which PC would crumble first under the load of the game. Make an offensive move on your PC that you hope will be the decisive strike that turns the balance of power and then turn to watch it on the machine of the other player if their PC was better than yours because your machine would simply slow down to nothing (seconds per frames, not the other way round) under the thousand of explosions and calculations around the 3D terrain rules (even if the ground was rendered via a sprite map and only the units were polygonal).
We, as many did (“Hey, non-aggression for the first 15 minutes!”), started out with a period of peace to allow everyone to at least get a footing (this is effectively something of a handicap for the better players to not just eat most of the resources at the very start) and build up basic defences for a core base. And so the lines of last-stands were brought into being. From there, many an epic battle was fought. Raids (on power or forward posts) vs establishing long-range artillery positions; radar vs blocking to prevent accurate locating of enemy forces and radar-based autofire of artillery; eventually into underwater bases and requirements for sonar as well as radar wars just to know where to shoot and what was coming. A thousand battles and many of them took on these last-stands as slowly a defence built over an hour was eaten away by the dominant force while the main strategic plays were around nukes vs anti-nuke missiles etc keeping the conventional war with front lines from being collapsed by super-weapons that could strike deep into the heart of a base. Defensive long range artillery you say?