Here is the issue in a nutshell. We can either:
- Give DMs leniency to make appropriate rulings, and trust that any rulings they make are for the good of the game, their players, and game balance...
- Hamstring DMs by providing a list of hard rules that must be followed, regardless of the cost. If a rule does not exist - the DM cannot make one up, and if a situation comes up that demands a rule (or rules change), the DM is SOL until a new set of rules is released.
- Take the middle ground.
4th Edition took the hard-line, and it was a disaster. Due to the kitchen sink nature of LFR, and the fact that the campaign relied exclusively on errata - whenever an issue came up in LFR that caused problems for the OP, the dev's released a new errata that affected ALL games. This would fix the current problems, but create new ones.... and would only work until the next loophole or rules exploit occurred. At that point, players would be free to run amok with DMs being impotent to make corrections until such times as the next errata was released and HOPEFULLY fixed the current issue.
5E takes a moderate approach. There are some hard rules which must be followed, and the rest is left to DM adjudication. The thing is, the hard rules are moderately extensive and despite being moderate - we are having serious difficulty getting DMs and players to follow those rules as is.
For example: DMs are allowed to adjudicate any ambiguous or unclear rules and create a ruling for that session.... Some DMs try to impose those rulings on future DMs, and some players refuse to accept DM authority in this matter. Then there is the FAQ which spells out campaign-wide rulings that MUST be followed, or the fact that DMs are not allowed to substitute monsters in an encounter (but they can add/remove existing monsters).
AL has very few rules which must be followed. We expect players and DMs to abide by the printed rules in the PHB/MM/Errata, the ALPG/ALDMG, and the FAQ. We also provide frequent clarification on how an AL-ruling is intended to function. The AL however, gives plenty of room for players and DMs to make the game their own.... For some, this is still too much restriction, and for others it is not enough.
We can't please everyone, but I think the moderate approach that AL has taken serves the majority overall.