Art Angels is her most artistically distinctive album to date- only Grimes could have made this combination of songs. Her earlier music is very derivative in comparison. It's possible to imagine a Geidi Primes being made by other people. There's actually a good reason the media ignored Grimes until after Darkbloom existed. Geidi is a very promising debut and Halfaxa is a masterpiece but both are also rather unoriginal and imitative of some other artists. Some artists with a lot of marketing behind them can get acclaim for far more derivative music (Tame Impala comes to mind), but when you're a DIY artist you need some originality to stand out. Grimes was big in her own city's underground scene, but when you put Geidi Primes against the history of music, you can see that it's (typical for a debut by an artist destined for later greatness) very well crafted, sincere, but still somewhat lacking in originality. Halfaxa is a bit more original, but it's still similar to what a lot of others in her generation were doing (and what others had done in past decades using different technology), and the main difference is in its higher quality, not its originality.
If these albums were her only legacy, Grimes would be forgotten, because the Cocteau Twins already existed, Gang Gang Dance and Dead Can Dance existed, and she wasn't doing anything radically new, just recreating those sounds in a more DIY way. Each album since she "went pop" (which started to happen with parts of Darkbloom, and more so on Visions) has been more creative and less like her influences, and draws from more and more unexpected influences all at once, creating a truly distinct Grimes sound which didn't exist yet in her earlier work. Even Visions, which is quite unique in itself, is more derivative than Art Angels. If there are dozens of other artists who might potentially have made a Geidi, and a few who could have made a Halfaxa, there are even one or two who might have made a Visions... but absolutely no one else can make an Art Angels. The album is unprecedented in music history, both for its sound and its process of creation. Each song on the album certainly has its influences (this is equally true of her earlier work) but whereas, on her early albums, the whole album could be explained as a pastiche of one or two genres or artists, and on Visions she's working with maybe five or ten genres, on Art Angels there are about 50-100 genres being mashed up together.
Her music has been getting more and more complex with time. Some people don't like anything with a beat or a dance rhythm, but that's also a new form of complexity that a lot of her earlier work didn't have. She maintained the melodic complexity and increased the textural and rhythmic complexity. Pretty much the opposite of a sellout.