Yup, they don't call it grimdark for nothing.
Something to bear in mind about that is Sanguinius himself. As a Primarch he has an obscenely high healing factor, so healing from blood loss or any injuries sustained from extracting is no real problem to him. I wouldn't know how much blood is used in those initiation rites, but you could definitely stretch something like that out.
Of course that ritual might not be a thing in 30k either, given Sanguinius is still alive. But don't quote me on that.
In a weird way it's kind of funny when you realize the Blood Angels are one of the nicer Legions; they care about baseline Humans, they do art and high culture, so on and so forth. Mind you when the alternative is a Legion who wears the flayed skin of their victims (Night Lords) or a Legion with berserker implants installed (World Eaters) the barrier's not that high.
As to the pauldrons... yeah you got me there for some of them. Heightened senses and reaction time to off-set that? But yeah, rule of cool (or more aptly rule of metal) tends to reign in 40k.