The best way to run Tomb of Annihilation is to ignore the Death Curse until later in the adventure (like when the party gets in the vicinity of the Tomb.)
In hindsight, I would've ignored/downplayed the Frostmaiden's curse in Rime of the Frostmaiden until the party was closer to dealing with it.
Having a party adventure for levels 1-8 with an earth-shattering calamity in the background seems silly when the bulk of the adventure content is devoted to exploring side quests in a large open world.
So in ToA, I would probably add a mid-boss warlord in the jungle for the party to find, or ramp up the importance of Ras Nsi. In RotFM, pick a faction early and focus on them (maybe the duergar) and have the party seek out Sunblight - and then have the winter curse happen.
Breaking them up into 3 or 5 level "mini-arcs" is probably the way to do it.
I'm curious about how I'm going to salvage RotFM at this point. I likely will just have the party end the winter curse and then move on to another storyline.