If there are 'lineists', there is likely such a thing is 'lineism', and that at least comes up with several hits:
Based on these and similar results, the term seems to be generally used to indicate a stylistic tendency to accentuate lines in artworks.
I also performed a search query on the Internet Archive, since the term could be outdated, and, indeed, there are some — but very few — hits:
In these articles the word is used in a more abstract way: the 'lineist' is someone who draws a linear or direct conclusion from something, or sees something in an all too straightforward manner.
Most notably for our context are the following quotes:
These are from a book about suprematism in art (coincidentally the same one as referenced in Danielillo's answer).
Since this seems to be the only hit when it comes to suprematism (or art history in general), it could be a translation of or neologism for a French, Bulgarian, or Russian word.
Looking into that did lead to finding the word "Liniizm" as coined by Russian avant-gardeist Alexander Rodchenko (also mentioned in Danielillo's post):
"We know that before Construction No. 126 was painted he had been working on a theoretical statement to be called Liniizm (‘Line-ism’ or ‘Linearism’), in which the whole immensely complex problem could be addressed."
However, that word has also (and more often?) been translated as 'linearism' (see this PDF of the article 'What is Linearism?' by Alexander Lavrent'ev, for example).
A few additional but not particularly relevant comments:
Quite a few of the references come from Latin texts, but - and this is corroborated by how Google hardly finds any hits with the query '"lineist"' - this is due to bad Optical Character Recognition when the texts were digitized (mistaking 'lineis' several times).
There is also the old rendition of 'finest': "fineist", sometimes misinterpreted to be 'lineist'.