You're not wrong, but "potentially losing actions" is very reliant on having unlucky turn order and can often be mostly or even entirely mitigated with lower level bonus action heals for which you usually have plenty if resources, getting them back in the fight without using your own action or your bigger spell slots.

Using other healing spells could potentially prevent your ally from losing an action, but at the cost of definitely losing your own and potentially more important resources. So it'd have to be two rounds worth of damage to even begin being worth it for the purpose of preventing lost actions and even then, that only makes it more useful in a pretty specific situation that requires multiple party members at risk of going down.

Hence my thinking that hit points having more value in general beyond "you briefly fall down if you lose them all" is needed before buffing healing spells would even really have an impact.