Well, in general terms, that is true.
But with specific electic plants, they do better in softer KH's, not GH's near as anyone can tell, many have GH's in the 8-12 range without issue for every plant species.
I melted my Tonia belem with 10ppm of Mg, but the high GH from SeaChem Eq or the GH builder from Greg Watson did not.
Unless you have certain plants your are interested in, it does not pay to bother.
KH is the main issue for the 5-8 species, out of nearly 300 species or more folks commonly keep.
We use to have 30 species tops when I started doing fully planted tanks, that was it. When I kept plant, maybe 10 species where available, Petco etc have more species in better shape today that was the case 20 years ago.