sorc bubble can shield for ~4k damage upfront, can be cast on the same target 1/17sec can be cast on multiple targets without cd
if single stacked hot would heal the same as double stacked then: it would heal for ~5.5k but it would not be upfront, could be cast on the same target 1/18sec could be cast on multiple targets without cd.
they would be similar, one would do a bit less shielding but it would all be upfront, the other would do a bit more but it would be segmented.
as a bonus for shield it isn''t affected by heal debuffs too, so in pvp it would still be better.
HoTs can overheal. Shields cannot. As such, HoTs should have a higher heal value per cast time (they are both instant so that's easy to compare) and a higher heal value per cost.