I have spent all my legendary shards and basically poor on focusing engrams or more specifically the gambit and trials engrams. I don't have enough to even focus the umbrals. I want legendary shards dropped from playlist activities because I don't play all that often nor have the dedication to farm up nightfalls for weapons to discard. The engram focusing cost for trials and gambit is also so high that I went through more than half my legendary shards focusing for mediocre rolls and the payoff is just not high enough to warrant focusing them.
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The Prosperity mods provide a decent chance of additional Legendary drops from playlists, and will pay for themself if you don't already have a fully masterworked Ghost. Unless you absolutely need to a piece of gear to be in the Pinnacle (1550-1560) band for an activity, for Grandmaster Nightfalls for example, using blue gear for infusion may equal more Legendary Shards depending on current habits.