There might be a dropoff point where you will not want to stack your offensive buffs. In an extreme example, if your first buff had an uptime of 6 seconds and you would cast 3 more buffs after, that first buff would run out without having affected anything. Of course, we wouldn’t do that and the numbers might work out differently, but you will always lose a portion of the first buff’s effectiveness because you waste a part of its uptime. There will propably be some dropoff point at which you wouldn’t want to cast 4 buffs consecutively because you lose too much buffed uptime on the first buff you casted. Could be that it will work out that, in order to maximize DPS, it is best to cast only 2 buffs at a time, get out all your damage abilites (most of which have their own cooldowns) and then cast the remaining 2 buffs after the first batch ran out.
I would only suggest that you try to set up some logic in the AMR simulator that makes it possible or easier to quickly predict, whether it is better to stack offensive buffs or have them in a specific order/grouping. This will also propably change all the time during BfA, when balance patches come out. It might even change from character to character, if talents or Azerite gear change the numbers on your offensive buffs. So AMR’s best in bags might have to remind a player “if you use this piece of Azerite gear, you should use buff X on its own, without stacking” So how do you feel about this at AMR? Is this easy to figure out? Would you maybe even add it to the BiB, in case this “dropoff point” will be dependent on individual gear?
*I know I am asking a hypothetical here that might only be relevant to a few specs. But maybe this is at least something you would run the numbers on once or twice, if there even is a dropoff when stacking/conescutively casting buffs vs. buffing and using damage spells right away to use buff time most effectively.