What do "branching options" really bring to RTS?

This question suddenly comes into my mind. Ever since RTS started to become “creative”, there is always some level of “branching options” that you pick during the match, unlike in earlier games where all the bonuses and abilities you have and can get are determined when you pick the faction. I’m only listing what I’m familiar with:
AOM: age-up options
AOE3: decks and age-up options
AOE4: age-up options
RA3: protocols
COH3: battlegroup trees
Their common feature is you have to choose some of the bonuses, often mutually exclusive (either strictly or effectively, where you don’t have enough time or resource to get all), during a match.

What I expected from games with such freedom, long ago before I became familiarized with them, was that one needs to carefully think about which to pick depending on the circumstance, or responding to the opponents’ gameplay. This should add another layer of strategic depth to the games.
However, in most of the cases, I feel that one already has a firm idea about which to pick the moment the match starts, depending on the map and opponent. It all comes to how quick and well you could execute that pre-determined build and how quick and well you could disrupt your opponent doing it.
For example, in AOM if you play Isis there is the really strong combo of Bast-Nephthys. What really matters is the timing, like when you age up, how many units and myth units you have when attacking, and when to cast the god powers. I wonder one would run into the circumstance of “oh no the opponent is using a different strategy. I need to choose the other minor gods.”
In AOE3 sometimes you need to emergency ship units for defense or counter. But again, most of the deck build and the order of sending cards is determined the moment you see the map and your opponent.

To clarify my confusion: yes you need to weigh over the timing and order depending on the circumstance. But you also need to consider which techs to research, which buildings to construct, and their timing and order. Now it seems to me that those designs are just fancier versions of the traditional tech tree. They don’t bring more real “freedom” and “diversity” to the gameplay as they seem.

So now I wonder, how different is it from the traditional RTS design where you pick all the bonuses and abilities before the match?
Or maybe it’s just because I don’t play pvp deep enough. If people have seen some high-level gameplay that really show this level of strategic diversity, I’d love to take a look at them.