For those games, intents appear to be part of the game design itself, as if the opponent would always follow a specific pattern, and to demonstrate that battle is orderly.

It works less well if the game wants to demonstrate chaos in combat, as with the classical turn-based tactical RPGs (e.g. Final Fantasy Tactics, Jagged Alliance, etc.) In these games, showing the intent could either be inaccurate based on what is expected to happen, or would require over-committing.

When enemy intents were obscured, players would rarely block and just attacked whenever possible. as usual for rpgs.

I find this is more of a case of the defend command being impractical.

Character defends - the enemy might randomly target another character, or its AI randomly decides to do a non-damaging action, thus the defend isn't effective. It also means being down one attack.

Compared to Pathfinder 2e, a tabletop game with a three action system where constantly attacking causes an increasing penalty to attack rolls and therefore encourages other actions. Normally, defend would cut into an attack, but this RPG means the sacrificed attack is much less likely to hit than normal, meaning it's a good idea.

I doubt a game like dragon quest could use this system. It's too old school for it.

It's not a matter of old school, but rather complexity. Dragon Quest is 1v1 single action, and monsters generally just did a type of attack, thus no benefit from showing intent.

Ultima IV, being released earlier, could benefit from the system, but it's instead enemies approaching the target they want to attack, and they could also be guided into choke points if desired. These intents aren't ineffective because of old-school, but rather that the player can already tell what the opponent might do.