Japanese animation isn't any more mature than Western animation, it's just that there's more of it. Basically, if 5% of Western Animation is 'good' and 5% of Japanese Animation is 'good', then sure, there's more Japanese stuff there, just because there's more of a base sample.
But as with anything, Sturgeon's Law applies. 90% of everything is bull[pudding].
And just as Western Animation is choked with Saturday Morning Toy Ads, Japanese Animation is choked with interchangeable (and interminable) 'struggle' series and harem comedies. Most of which are just as interested in selling product.
And there's nothing that says an animated series aimed at 7 year olds can't be good.