Well it depends on the shrimp too. RCS will eat a lot of your algae but not all types. Amano shrimp eat a lot of types of algae and a lot of it as well. Yes they will clean your plant leaves too. CRS and all those other shrimp eat more of the uneaten fish food/poop etc etc. The dead stuff. Filter feeding shrimp obviously only eat floating stuff so they'll filter your water and eat floating algae/food all those good small floating stuff.
I dunno about clown loaches. I would say 100% better than clown loaches if presented in good quantities.
a key issue in a planted tank is plant and gravel disturbance.
obviously a group of shrimp are less disruptive than a loach,
and shrimp will clean upper plant leaves a loach won't go to.
loachs also eat Ramshorn snails which may benefit a planted
tank, while shrimp won't disturb snails at all. so if I had a
choice between a dozen shrimp and one loach, I'd get shrimp,
however for some loachs are easier to keep, as shrimp are so
sensitive to water impurities that many can't keep them long.