This theory begins to break down quickly when you are fighting creatures that cannot speak. Do dire wolves telepathically let one another know when ninjas are afoot?
This was part of my original post.
(in certain circumstances a DM can decide if that is appropriate ie: if the creature cannot yell/signal in anyway your DM may decide to allow you to remain stealthed against the other creatures)
But remember that having a stealth advantage does not always imply the creature is completely hidden from the world it simply implies it is not being noticed. Whether or not the creature is completely hidden or just unnoticed depends on the situation and your DM. Again say someone was sneaking up behind you and you do not notice. I yell "Hey behind you!" a quick glance reveals a previously unnoticed elderly man with gas encroaching upon you. You are no longer unaware of said dire threat.
Situations vary by the vary nature of the game, your DM will decide what is and is not appropriate for each situation. There is NO need/way for EVERY single possibility to be accounted for and as players/DM's we are expected to exercise common sense. Unless you have a Wisdom score of 8, then we understand.
Furthermore you do not SEE a ninja.
Furthermore, furthermore having cover OR concealment is STILL grounds for a stealth check.
It seems to be that the problem isn't within the rules it is within the people who refuse to apply common sense to situations and adjust rulings accordingly. A dragonborn hiding behind a halfling is a common sense/DM decision. If you are upset that your DM will not allow it EVEN THOUGH it says nothing about you not being able to in the core books then leave the group as everyone else probably hates you and does not want you playing with the group anyway.
As for the warlock flavor text and whether or not shadow walk is for a pseudo-defense bonus, and other worldly questions about what it
really means to be a
warlock is irrelevant to this topic. Bottom line shadow walk conceals a warlock and if it makes a stealth check as part of that action it gets -5 on it's check PERIOD. Though agreeably more detail about the shadow walk ability would be helpful. Remeber don't just ASSUME it DOESN'T obscure the square either. Untill a better explanation, best bet would be to let the DM decide. However amazing or expressly lackluster you want the effect to be is also up to your DM.
"The warlock grows dim and glides across the battlefield, melding and weaving into a darkness whose source cannot be defined. The kobold is startled as his previous target is now but a flicker of a shadow dancing about. A semblance of death incarnate"
OR seemingly as you would prefer
"The warlock has concealment now ... hey can I have a Mountain Dew?"