Disney canon has no importance when comparing PT characters to Legends characters from other eras.
SoD Maul level was a conclusion I conservatively reached for SoR/KOTFE HoTlander to make the point that even if he is only SoD Maul level, Vader being above prime Outlander becomes a ridiculous notion. What the HoT did in Act III against a more powerful Vitiate than the one that brought down a large portion of the Dark Temple (under extremely disadvantageous circumstances) and the assessment we can make for his dueling abilities from his raw power+battlemaster accolade is more than enough to compare him to the likes of Dooku, and perhaps even Vader himself.
Don't forget that this guy becomes the supreme leader of the galaxy in his twenties. His coming was prophesied 300 years before his birth. It's no surprise that he outshines Vader. Even the gigantic gap between him and Valkorion has decreased significantly.
Based on all of this, Arcann is EASILY Vader level, and the Outlander is significantly above that level. Get over yourself and realize how much more powerful the Outlander has become since early-KOTFE.