Legacy Moveset Value

I’m holding off TMing some legacy sets in hopes that a reworked battle system is eventually included with the possibility of having different moves possessing different effects.

For example, ancient power in the main series carries a small chance of raising the user’s stats by 1 stage (initially boosting them by 50%). If Go ever implements such additions to moves (not the same as the main series, per say) then I will be happy! Otherwise I’ll be holding onto mons that will essentially be collecting dust, not stardust.

Is it the most efficient way to play? Nope-but it makes me happy

Gyarados is about to be completely outclassed by Kyogre as a water attacker. Sure, Gary's flying typing gives him double resistance to ground, but at the expense of piling on another level of weakness to electric. So if your motivation is having a strong relevant water attacker, don't worry too much, and catch yourself some WF/HP Kyogre when they come out.

I'd just sit on them. Surely there's room in your Pokemon Storage for 4 old, slightly washed up warriors?

Legacy moves are often a tradeoff (usually for the worse though). DP has a better damage window and is faster than Outrage, but is overall worse. The Double Legacy is definitely more valuable, so I don't see the need to keep B/DP if you really want Waterfall.

I have a Diglet and Dugtrio both with Mudshot....among others

I know they are useless...but that means that the majority of people who had them have long since got rid of them.

Personally, I like to keep legacy mons - it is not like I am going to have a lesser gaming experience because I have a few pack slots dedicated to keeping something that no one else will ever be able to get again.
I have even evolved Ash Hat Pichu so I have an Ash Hat Pikachu with 'present' - so when the event is over and 'Present' goes legacy I have mons that have the move that never got it in the first place.

My non-event shiny Pichu got evolved to a Pikachu so I have 'Present' on a Shiny Pikachu without any event hats - she should be fairly rare too as a female is rarer than male in Pikachu.

If you are the type of player that needs to justify every spot in your pack as being totally meta relevant, then perhaps most legacy move sets are not for you.

Is Bite a legacy move for Gyary? I could have sworn it was Dragon Tail.

SC on Gengar, the best example of when legacy is better than current available. I maxed mine and i place alot of value on it.