I fail to see where a 'brush' differentiates from a 'stock' image. BOTH are pre-drawn/made/painted/created images taken and used.
Whether it's copy/cut-and-paste from someone else's art... or an included image built/found within an image generating proggy it's still going to be ONLY as good as the vision of the user.
Cutting and using 'any old blob' of graphic MUST be done with an understanding of [in the case of landscapes] Nature.... of space... perspective...depth of field .... lighting.... atmospherics even, when clouds, sun, shadow, etc are involved.
Attention to detail.... like making sure you are NOT cheap-shotting the work by cloning - is what makes the difference between point-and-click image generators and actual HUMANS doing the work.
Again....those clones can be concealed by MANUAL editing. This image SHOULD be a SINGLE Bitmap [even if it isn't yet...and comprises layers]....when it's a single bitmap it is IDENTICAL to such critters as Mona Lisa - each bit belongs to each other bit...and can be blended and worked as a whole ... and not lose its sanity and direction in a sea of layers.
Image generators and other 'shortcuts' have no intelligence, vision or soul. They are machines. Machines [by definition] do NOT create art.
The VERY FIRST time I saw a fractal [probably decades ago] I thought "wow...the mathematics of line generation must be insane".
At no time did I think "wow! masterly Art".
Those cloned 'grass' bits..... they are as valid as clipart in Word95 .... Junk, mostly, that cheapens the result.