Hindsight is 20/20 they say. Here is my two cents, which are probably worth even less than that. With Daemons being designed as a hordes army, any further rule which bogs down the game should have been avoided or minimized. Games Workshop, for some reason, have concluded that people really like bogging down. They appear to have assumed that the last ten years of people saying they DON'T like it is really a case of "methinks the lady dost protest too much." Oh, well... go figure. I'm not against all random. I'm for doing it in a way which doesn't slow down the game and by which the players have some control over events.
Random elements, for the most part, should have been determined at the start of the game.
*By this I mean the countless variations should have been determined (via gambling) before the start of the game as they are in the new CSM book. Daemons, being even more chaotic, should have possible greater gains and losses, but only one roll should be used to determine these things for the duration of a given game. I would have created a rule called Warpstorm for all Daemons. There would have been three charts called LOW RISK, MEDIUM RISK, and HIGH RISK. At the start of the game, each unit must roll on one of the charts (player's choice). The rewards and penalties are determined by the chart selection. The "Low Risk" Chart would statistically result in no benefit far more often and have gentle punishments or perks scaling on the roll. The "Medium Risk" and "High Risk" respectively would increase the potency of the rewards and punishments as well as scale up the probability of getting them. Think of it as a bit like Dark Eldar combat drugs, wherein the player gambles. Either way rolls and gambling is done up front as is the marking/tracking. It should be noted that this is still extra work. It will still take an investment of time.
If I were doing this (as above) I would also have created God-specific charts. Why not? That way if you use Nurgle Daemons they get to roll on the Nurgle Low, Medium, and High charts. I would have dumped the random roll every shooting round entirely and had some of the potential rewards and punishments cover those things. For example, one unit might have rolled the penalty on High Risk which means any Demonic Instability test it takes is at a reduced Leadership (or perhaps adds a die against them). Perhaps a reward to a Tzentch unit is that any Deny the Witch roll that succeeds requires the attacking non-Daemon Psycher to make that Leadership test on 3D10 or be removed and a new Herald arrives. You get the idea. This, at least, would not only have kept these element but it would also have made it less irksome to people you play against. They could choose NOT to try to use their powers on a given unit rather than just starting the game and losing a Character for no other reason than a die roll.