Interesting that out of the two races, the one dedicated to chaos and evolution through violence and conflict is the one that is the physically weaker of the two (relatively speaking of course.) Even at a technological level the Vorlons appear to have had the upper hand. While on the one hand the Vorlon Empire supposedly encompasses a huge swath of the galaxy, which they appear to be able to defend with an almost casual ease, while on the other hand the Shadows are repeatedly beaten back (or allow themselves to be beaten back) to a single world out of the very edge of the galaxy and are so poorly defended, primitive alien ships can land without doing much more than setting off the burglar alarm. Indeed, you have to wonder why they need to go into these prolonged states of hibernation (besides it being a plot contrivance of course.) Were they not able to crack immortality the way the Vorlons did?
Why would Shadows want to be immortal? The way I interpret it, they know there's no evolution or adaptation if they don't die off and reproduce, or at least meet with struggle and reinvent themselves on regular occasions. Added to that their philosophy that meaningful growth only occurs through conflict, war and pain, and it makes sense to me that they keep themselves somewhat vulnerable. I always assumed falling back was part of the plan, a way to keep themselves in the evolutionary game.
The Vorlons aim for Order and a static perfection, thus they try to make themselves unchanging and perfect - "we have always been here". The Shadows, I assume, try to better themselves their own way - which involves struggle and trial by fire. Taking a hit to the face, leaping back and then coming back later, strengthened by the experience - all very Shadow. Let the stuffy, stagnant Vorlons gain immortality and invulnerability and thus become an evolutionary dead end! Perfect? Pah! All they've done is remove themselves from the natural order of things entirely! And they have the gall to think that wisdom? Leave the younger races in their hands? Madness!
I assumed the hibernation periods are a part of the agreement and work to the Shadows' advantage. The Vorlons spend centuries building up Order, encouraging co-opeation within a framework of Knowing Your Place, guiding the younger races towards a static "perfection", and then when the pieces are in place the Shadows return and gleefully aim to tear it all down, first undermining the Vorlons by getting the pieces to turn on each other and tear the Order down from the inside, and then just tearing into it themselves. I assume they actually want the younger races to put up a reasonable fight against them as well as against each other - it's when the younger races
won't fight that the Shadows get enraged, unlike the Vorlons, who hate any sort of resistance to their whims. It's only when Sheridan started
uniting all the young races against them that the Shadows decided they had to interfere and try to stop it. I assumed fighting back yourself is good - let's see if you're strong enough! - but relying on each other is "cheating" somehow, as it shows a disturbing tendency to choose order over chaos and ease life rather than encourage the conflicts needed to help a race grow as a people.
When the Shadows were driven back by the Minbari 1,000 years ago, I guess they were probably happy about it - "we've just inspired the Minbari to greatness! We're liberating them from Vorlon servitude by making them see that strength comes through conflict and struggle. They even gave us a bloody nose in the end - good for them. Now, let's retreat to our hibernation and learn from our experiences this time round. We'll reinvent ourselves next time".
I assumed that part of the reason for the name "Shadow" is that they originally altered themselves based on the Younger Races and not vice versa like the Vorlons. The Vorlons want to control and manage all the Younger Races. Whatever new cultures arise, the Vorlons go on being the same and trying to bend those races to their will. The Shadows, though, no doubt alter their behaviour with each new culture so as to find the best way to encourage conflict (like in the final debate, taking on different forms each time they approached Delenn to speak). They manipulate from behind, while the Vorlons dictate from in front. The Vorlons are the light everyone turns to, and the Shadows are the darkness constantly trying to turn them away.
So I think the Shadows probably keep themselves more vulnerable than the Vorlons deliberately, and I don't think that contradicts their desire to cultivate strength given that it's all about change and evolution. That's how I read it, anyway.
