The strategy of RTSes is strategy of big plans and high level abstraction

That's not true in all RTSes. Take StarCraft, for example, and there are plenty of games on record that were decided not just by 1 unit, but by 1 attack from 1 unit. There are Zerg players, for example, who have developed a reputation for creating havoc after getting a single zergling (the smallest and cheapest attacking unit) into their opponent's base. A single shot from a Protoss reaver can mean the difference between taking minimal damage and losing half of your workers (and subsequently the game).

Sure, StarCraft is kind of a hybrid when you think about it. The guaranteed-hit model, the extremely simplified low vs high ground approach to determine if a shot is possible, etc. are pretty deterministic. But in more complicated situations it's still a lot less predictable than chess. Even the examples you're giving can only happen probabilistically outside very early game.

But I'm thinking about TA-style games, the topic of this discussion, which pride themselves on large armies. Though, to your point, early game of Supreme Commander is also quite chess-like, because of how restricted the set of opportunities is.