agree, being done both 10 and 25 as a healer and also in DPS, 25 is way easier in most fights
if a healer DCs in 10man is usually GG if a huge damage comes, in 25 you have more 4 healers and 4 Cds, if its Stacked damage then it becomes even more easy to handle it
DPS is more needed on 25 only the 2 weeks of new content, max 3, after that Dps in 10 man have more responsibility to pull their numbers (drops sucks in 10 man)
so the final is 25 is only harder in the first 2/3 weeks and only harder if the encounter require constant /range and small spaces (blood queen, alk'ir, ...), the rest if face roll
its only not face roll if you have to carry 8 slackers