This is a really interesting question!

For carboxylic acid and ester conversions, I would say both species are roughly equal in reactivity depending on the pH (as the leaving groups OH- and OR- are pretty similar). However, you still have the problem where you do need to "push" from one to the other.

To push from an carboxylic acid to an ester in a Fischer esterification, we flood the system with TONS of ROH (for example to make a methyl ester, we have our solvent as MeOH, and no water in the system). as well as a catalytic acid.

Because there is tons of ROH around our carboxylic acid, soon or or later the water will get kicked off. If we add a dehydrating agent to mop up water, we can also remove it as soon as it comes off. This drives the reaction forward using Le Chatelier's principle.

Any time that we run into reactions which are going from a less reactive to more reactive compound, we have to couple them to a favourable process, just like in biology (anabolic and catabolic reactions).