So piecing all of the information together.
In a recent video in Sevtech Lash has explained that Brian is not a person but a fluid. But this is not the first time humanity has spoken to inanimate objects, as we do it do our phones all the time. So my guesses are that there is some person behind Lash.
Then there is a past Lash who made 2×3 nether portals. This is the Lash from before he said that a 3×3 portal is the minimum standard of his channel. This past Lash doesn’t have the weird MC Eternal guy or other really weird behaviour, but he does like to call himself pretty.
There is the current Lash who makes videos with better thumbnails, and he often faces off with unusual threats such as the MC Eternal Guy. It appears that this new Lash “evolved” after Lash got a computer upgrade and switched to Windows. One of the “downsides” of this evolution is most certainly the MC Eternal guy. (But note to readers that the MC Eternal Guy has been foreshadowed in previous modpacks like Enigmatica 2, where Lash fights off an alien invasion full of Thaumcraft people while riding a black dragon.)
Then there is Lukas who manages to manage this forum and the discord and the blog and the wiki. Which is a lot of work. The interesting part is that Lash is starting to slow down on replying to Youtube Comments, and he is taking massive weeks-long breaks in between sporadic video uploading sessions.
This has led me to believe that he is in fact Lukas, and he is overwhelmed by the difficulties of living a dual life. Hence he needs weeks long breaks to have time to prerecord videos and act as Lukas, and then a few weeks where he is busy on YouTube acting as Lash. Therefore, Lash is Lukas and Lukas is Lash, the same person but slightly different purposes and responsibilities.