Hey there Fox in a box
The reason he included we are legion and master of sorcery is because he also included bolt of tzeentch, meaning the herald can split fire both ranged attacks, meaning you can pop a transport w bolt and then shoot his damonic gaze at some infantry if required.
The tzeentch herald on Chariot is generally considered the best
HQ choice for the points value.
Anyhow looking at your new list, its an improvement however there are a few adjustments i'd make.
Flamers - wouldnt give the flamers bolt - generally flamers are a suicide unit, its very rare the last longer than a turn or two on the board given the threat they present. Your paying alot for one or two bolts for that. I'll get into what you should spend the points on in a moment.
Skulltakers a bit of catch 22 at this point - He can be very effective, however his forte is killing characters and big nastys - at 1000 points there isnt going to be alot of stuff out there that fits that criteria and the fact is, whatever he can handle - it is likely at a 1000 points the 'letters or bloodcrushers can handle too. You also need him in a squad or he'll be killed - meaning more points required to bubble wrap 'em, more points on an already expensive character and unit. Dont get me wrong - whatever that unit touch is toast - but it is prob overkill at 1000 points. I'd look at getting some crushers and perhaps making herald on juggernaut or a Tzeentch herald on chariot - its your call though, i have the model and field him in friendly games.
The horrors - i'd split the squad into two 5 man squads both w bolt and one with the changeling. Use the points for the bolt from the flamers.
Ultimately its up to you what you wanna do. Hope your list works out well