Not only we believe they are better but others also believe. We can buy weapons from US, Russia, France, UK or any other country which produces weapons. We do not have the restriction like china or pakistan so we shall buy only the best. Now suppose we buy S 400 form russia. If it is not good than why china bought it inspite of having Hq9? Why china bought Su 30 and Su 35 in spite of having 5th generation plane (So called)? You problem is that when you or CHina buys something, it is great. When India buys it, it is bad. When Pakistan bought T80, it was most lethal tank but when India bought T90, it was an ordinary tank.