Why should any top end trinket be guaranteed? Sidereal essence is only there to preserve 239 loot, because 10ppl Ulduar drops 232 loot now. BTW you can double down on Scale of fates since it drops in 10 and 25 now. 252 BiS items of this phase for some 5-10 days of dungeon farming is an overkill of course. Besides Vesax and Thorim are two of the easiest HM bosses and you can skip strait to them.
What Blizzard should had been done with phase 3 was to make HM bosses drop 252 items only, not 232 trash (SoF should be farmed in none HM mode). We are getting not 4 items worth of difficulty but barely more than 1 per 25 ppl and it feels like Classic MC where 40ppl would get only a couple of drops to share among them.
However ToGC can’t satisfy raiders thirst for content untill ICC alone so they won’t make that loot rules change.