What are some player-created problems you know of? What are things that other players can do to solve them, and/or what have they already done?
I can't think of any.
All the problems that people attribute to players exist because the underlying mechanisms of the game do not provide players with the agency to counter them, without relying on out-of-context means, that may well amount to more severe problems themselves.
I don't think anyone would mind a rework to Fdev's crime and punishment system, but I doubt it would be a 100% solution, either.
Such solutions aren't required, because such a solution would result in an equally absurd system. Ganking doesn't need to be absent, it just needs to make more sense.
are there lawfuls or others that sit at Deciat to escort traders/explorers and counter-gank known gankers?
There are frequently "lawfuls" that sit at Deciat and occupy the attention of gankers, because that's the only vaguely effective, contextual, way to counter them. The instancing, travel, interdiction, combat, and escape mechanisms make 'escorts', especially within a single system, very difficult. It's a case of the tools Frontier has provided not being suited to task.
A PvP solution to the problem would require players to spend time waiting for the call to action - and, given travel times both interstellar and in-system, they would very likely arrive well after the fact (if the instance in which the targeted ship still existed that long after its destruction).
Only because of the utter lack of consequence (something else that is wholly Frontier's responsibility) renders any form of proactive defense, or attrition, unachievable.
In any plausible setting, the overriding reason for initiating hostilities against an entity is to cripple it's ability to continue, or initiate, threatening behavior of it's own. From the
mano a mano street fight, to conflicts between global superpowers, degrading the enemies' will and/or ability to continue is usually the whole point of violence. This is categorically impossible in the current state of
Elite: Dangerous. We have the tools for violence, but violence itself has little corresponding utility...and this extends well beyond PvP.
The solution (PvP or otherwise) that should exist, in any credible setting, would be to hunt perpetrators down and either kill them (in a permanent or semipermanent fashion) or render them too poor to continue their hostilities. This, in turn, would have a deterrent value.
If this galaxy really is one where everyone attacks everyone without warning or reason, then why do sidewinders exist? Shouldn't every ship be built to withstand such a thing by default?
The Sidewinder is a pretty safe ship. One of the smallest profiles in the game, room for plenty of armor, and able to made quite fast. My CMDR has a Sidewinder and the convergence of circumstances required for that ship to be destroyed approaches the absurd.
Still has little reason to exist in a setting where it's nearly impossible to suffer a setback that will provide the means to get a more capable vessel within thirty minutes of launching.