Hi Matthew, just caught this!
No, pointless digging out horsetail during it’s growing season under mulch. The whole idea of light exclusion is to let the plant try and grow; that way its parent root is exhausted as it attempts to grow constantly without light. With horsetail and bindweeds etc. it’s the parent root that is too deep to dig out, so mulching is a reasonable alternative. I believe it will tire the plant more effectively than constant foliage removal, but I could be wrong – Charles? HTH