More data. Euclid is for filling databases with survey data covering large-scale structure in the universe. Webb is for looking at very small, very distant si

More data. Euclid is for filling databases with survey data covering large-scale structure in the universe. Webb is for looking at very small, very distant single objects. Two different instruments for two different experiments. Consider comparing a fancy DSLR with a telephoto lens to a night vision security camera. Each does what the other can't, and you deploy them for different tasks.