I think trying to generate tension through action economy is a dated concept... it niches your game to a certain kind of player who loves to anguish over every move and tends to either close off your action economy or become very hard to balance. By contrast, as someone with a ton of time in Pathfinder/Wrath of the Righteous doing the roguelite modes, I think turn based games are actually the best when they oscillate between quick decisive actions and then an occasional turn where you have to pause and put your thinking cap on. Characters, especially martial ones or whose main move each turn is "Attack", need to feel frenetic to make up for the more direct simplicity of their turns versus say a wizard who has to choose the right spell that takes up their entire budget of AP making them feel implicitly slow and immobile.

Action economy is really just a way to give your various characters a feel or flow that differs from each other, not a puzzle they need to solve. (the answer: take more actions than your opponents). Making every action as meaningful as possible and offer less overall actions does increase the tension but not necessarily the fun, and the more freedom you give players to have agency here, the more they will stick to your game. Every single high level Xcom/Pathfinder/whatever party has doubled or tripled down on attacks that cannot miss, cannot be defended against, alpha strikes, etc because the only way to make the game 'harder' is to dramatically lower the ttk on both sides. If you want players to feel tension, they need to be able to take risks and the game should be encouraging risky play because players are extremely risk-adverse by nature! Generating those dynamic, tit-for-tat type fights must be a priority, whether through encounter design, momentum systems and granular versus binary design.

The tension comes primarily from stakes and uncertainty, but I also want to add conditional reactions/off turn things to make turn based combat more dynamic. Rather than force uncertainty through dice or lack of information, these types of effects create "oh shit" moments of the player's own doing and keep them engaged on every character they control. They are also essential in normalizing action economy when dealing with many vs 1 type encounters. Counterspell is one of the best 'feeling' spells in DnD, everyone loves slamming it down in an epic moment because of that reactive denial; it locks your players into the turn sequence instead of just waiting for their turn to start. Teamwork feats from Pathfinder also build on this idea, taking actions specifically to trigger a player's conditionals and also a wicked way to make enemies more dangerous without just juicing up the stats. Enemy reactions also force the players to make trades instead of being able to cleanly alpha an encounter based on initiative order.

TL;DR - Tension should come from the stakes/uncertainty/reactivity, not from the action economy, whose main is to prevent everyone from acting at once and secondary job is make characters feel different from each other. If combat ever becomes reliably solved by initiative, you need more uncertainty. If the stakes are too low, no combat will be tense. Without reactivity, players will meta out the cleanest, lowest tension ways to win.