While I appreciate the effort it must taken for you to write this, your points can be disproven quite easily. Don't take this as a personal attack, these are merely my counter-arguments in this debate. Here goes:
1. Type: Null and Silvally are genderless and they are part of the Udiscovered egg group. This is an egg group that only legendaries and 'baby' Pokémon are a part of. (eg. Togepi, Cleffa, etc) No Pokémon in this egg group can breed at all, not even with Ditto.
2. Pseudo legendary Pokémon all share a three-stage evolution line, 1,250,000 experience at level 100, and a base stat total of exactly 600. While I don't know about the experience amount required for Silvally to reach lvl 100, none of the other requirements are met, so Silvally is not a pseudo legendary. Also, every pseudo legendary can breed with a Ditto at least.
-Besides, Kommo-o seems to be the pseudo legendary of this genereation anyway.
3. The fact that there are three known Type: Nulls does not deny their legendary status. Afterall, the player is only given one per game, and the fact that there are ONLY three Type: Nulls in the Pokémon world would make it quite the rarity; only legendaries are this scarce. Now you may be thinking that this cannot be true because more than one exist, but there are canon examples of there being more than one of the same legendary Pokémon.
-In "Pokémon the Movie 2000: The Power of One" there are two Lugias.
-Now in case you don't count the show as canon, there is a notable in-game example as well. Arceus made Dialga, Palkia and Giratina, and is said create new ones in case a trainer catches one of them. Also in HeartGold and SoulSilver, there is a special in-game event where Arceus itself makes a Pokémon egg for the player containing either Dialga, Palkia or Giratina at lvl 1. Therefore it is safe to assume that there are more than one Dialga, Palkia and Giratina out there, who are all legendary Pokémon.
4. Now don't hold me to this, but somebody once told me that Type: Null and Silvally are classified as legendary Pokémon in the games' code. I admit that this is my weakest argument, because I don't have a source for it.
In conclusion, the more people I talk to, the more it seems to me that Type: Null and Silvally are legendaries.