They refer to DOAX as a spin-off series, meaning that isn’t canon. Also I need to prove that the main game (Being DOA1-6) are canon? Is this a joke?
Spinoff =/= non-canon (not necessarily, anyways). I can actually name a few spin-offs of various franchises that actually ARE canonical. Like for example, Resident Evil: Code Veronica was marketed as a spinoff for the franchise, and that played a pretty key role in the plot of the overall games due to Wesker coming back from the dead and what not (of course, that being said, Code Veronica was actually intended to be a main series game, but the Capcom executives insisted on making Resident Evil 3: Nemesis, the intended spinoff, into a main series game, and guess what, Nemesis proved to be canon as well), as well as the Revelations and Chronicles games (heck, the Survivor games as well). Same goes for Metal Gear Solid: Portable Ops, which was directly referenced in Metal Gear Solid 4 and even the likes of Peace Walker (Miller specifically mentions San Hieronymo Peninsula in the latter game at the beginning). Heck, technically, Peace Walker ITSELF is a spinoff (certainly not one of the numbered main games, though Kojima considered it one in spirit before MGSV came out), yet that proved to be canon. And that's just going by games. Also, the Mega Man Xtreme games, which are explicitly canon despite being spinoffs due to Mega Man X6 explicitly referencing the events of Xtreme 2. Same goes for Pokemon Ranger, a spinoff, yet at the very least the first game was canon to the main series thanks largely to the whole Manaphy side-mission thing and it being directly connected to Diamond and Pearl's plotline. If we go by other mediums, the NCIS spinoffs are given crossover episodes with their parent episodes (and in fact, many of the actual premieres were in their parent series as backdoor pilots via crossover episodes), and Pokémon Chronicles and the various Hoso specials are explicitly canon to the main Pokémon anime.
Not to mention, being a main game =/= canon as well (again, not necessarily). Metal Gear and Metal Gear 2: Solid Snake were main games, yet thanks to a lot of retcons made by Kojima, to say little about a marketing timeline released during Peace Walker's development, they barely came across as even slightly canon, basically being non-canon in all but name. And there are even people who claim that Mega Man X7 and X8 aren't canon despite technically being main games due to Keiji Inafune not being involved in their production under any capacity (that, and Axl not being referenced in any of the later games barring MAYBE the reference to a destroyed space elevator forming Neo Arcadia's primary base). And that's not even counting explicit remakes to past games that decanonized them such as Star Fox 64 to Star Fox, or even REmake/REmaster to Resident Evil (possibly even Resident Evil 2's remake to Resident Evil).
So if you're going to claim DOAX is non-canon, you're going to need a LOT more than just claiming it's a spin-off to prove it isn't canon, because I just gave you plenty of examples of spin-offs in various other mediums that actually are canon, not to mention main entries that AREN'T canon.