If the engagement is over in one second, then there's no time for the player's (generally non-strategic) micromanagement ability to affect the outcome, and the result is only dependent on those pre-fight factors which I'd call strategic in nature (although execution barriers may be involved with accomplishing some of them).I'm going to have to disagree strongly that long living (that extend engagement time) negatively impact any of those points.
Individual fights being over in a flash favor the strategically stronger player who
- has seen through the opponent's strategy and unit movements ahead of time
- has successfully concealed their own plans and/or deceived the opponent when there is something to gain from it
- has made good choices in army composition, production capacity, upgrades, etc. in relation to their own strategy and their idea of opponent's strategy
- has correctly judged the outcome of a potential engagement before it happens, and avoided as many unfavorable ones as possible
- has maximized their positional and timing advantages for the fight before it happens
High life and low damage causes pretty much all of those to count less. It favors the player with the ability to make simple optimization decisions as fast as possible, and has the mechanical execution ability to carry them out (whether those actions are going to micro or macro). Suppose you are completely terrible at strategy, and have a habit of getting outplayed positionally and walking your army into an ambush. If you only lose 10% of the strength of your army under fire before you have microed it to regroup on a neutral footing, you can pretty much ignore positioning and still win most fights as long as you have a slight efficiency advantage from mechanical micromanagement during battles.
whether an action is over in 1 second or 1 minute doesn't change any of those things. Having the right assets in the correct position of the map at the right time is still king. If anything long engagement times forces many of those issues to be that much more important as compared to over in a flash combat.
Having the right elements in the right positions at the correct time is still important. Being able to move a squad of riflemen into a part of the map and know that they're not going to simply disappear the second the first 'counter' unit happens to randomly wander by means they become an important aspect of the battlefield, and that unit has to actually be considered. A long lasting unit won't be annihilated simply by random chance.A "counter unit" does not randomly wander anywhere; it has been sent by the other player for whatever reason. Depending on the game, various strategic skills can be involved in producing the outcome. Did the players scout properly? How were the players' decisions to send the riflemen, and to send the "counter unit", informed by the players' understanding of the game's probability space in general, and their ability to read the specific opponent? In the end, there's always some randomness of outcome in a game of hidden information (= practically all RTS games) even with mechanics being fully deterministic, but there may be surprisingly little of actual randomness left if you consider and eliminate all other factors. Even then, the randomness tends to very much average out over the course of a match.