There is Trellism and there is Trelagism.
The 'agi' part of Trelagism sounds familiar like 'urgy' of 'Hemalurgy' and it also sounds like 'ati', as in Ati and Atium (idk what hemalurgy could have to do with this but it's interesting nonetheless to Me).
In 'Lerasium' the 'asium' part sounds like 'Atium' and if you remove the 'Trel' from 'Trelagism', and Miles called the religion Trellism isntead of Trelagism for some reason so it could be relevant, and you have 'agism' which sounds a lot like 'Atium' too.
L - eras, Lerasium, Atium ('atium' resembles 'asium')
L - 'lagism', Ati (as in Ati from 'agi')
I think that Leras and Ati were actually the same person and that's why these similarities are so striking (well to Me at least) and that is why it's said, like by Allik in BoM, that Preservation and Ruin were always together, the same, yet always apart, and He/She is returning as Trell to be or bring about Discord.