Whereas it’s true that shade will decrease evapotranspiration of coffee, readers should be reminded that the shade trees themselves transpire and that when added to coffee, evapotranspiration per unit area is mostly higher for agroforest than sun coffee. Dr Vaast, a noted coffee physiologist, once told me as much and published research bears that out.

“Coffee transpired more per unit leaf area in full sun than under shade, an indication of higher environmental coffee stress in non shaded conditions. Nonetheless, coffee daily water consumption per hectare was generally higher under shade than in full sun due higher vegetative growth of shade-grown coffee plants.”
Van Kanten, R., & Vaast, P. (2006). Transpiration of arabica coffee and associated shade tree species in sub-optimal, low-altitude conditions of Costa Rica. Agroforestry Systems, 67(2), 187-202.

This is not to say that shade trees always compete – there may well be cases where they help coffee through the process of hydraulic lift from deeper soil zones that coffee might not reach for example.

The problem is that each locality is a complex of soil type, mix of tree species, micro and macro-climate. This makes it very difficult to provide helpful advice to farmers, especially when we no longer know what future conditions will be like – e.g. severity of future heatwaves, El Niño etc.

This also makes it problematic to talk of heroes and villains.

More trees are definitely needed in most coffee habitats, the question is where do they fit best? This thoughtful post is maybe worth considering: https://www.coffeehabitat.com/2020/11/integrated-open-canopy/