As an OG fan, I would prefer the blood and gore to return, because that's what I grew up with. That said, there are plenty of people who got into Halo many years after I did and don't care that much about blood and gore.
I don't think you should imply that people who don't care for blood are new to the games. I'm sure there are plenty of people who've beaten the corpse of an Elite in CE long enough that the framerate gets halved, but don't care about blood. Because the reality of the situation is that, sure, that's fun, but it's really not all that relevant for the experience. Apart from trying to break the game and doing weird art projects, there is really no value in enemies spraying massive amounts of blood. It really just makes the violence look more exaggerated and cartoony, which you may or may not like, but I personally don't care for much one way or the other.
This has been mentioned in a previous thread, but I don't think the ESRB rating weighs blood and violence as heavily as people think. If I recall correctly, the older games got the M rating thanks in large part to offensive language. I mean green goop from the Flood isn't blood, so I don't think the ESRB cares all that much about it. I could be wrong, but that's my two cents.
Language isn't the deciding factor. CE doesn't even have the "Language" content descriptor and Halo 3 has "Mild Language", the same as Halo 5, and so on. There's no single reason why Halo games other than Halo 5 are M rated. For the original trilogy Flood gives the "Blood and Gore" content descriptor instead of just "Blood", which may possibly by ESRB's internal guidelines elevate the game to M. Then again, Reach and 4 only have "Blood", but are still M, though Halo 4 may be explained by the human disintegration cutscene. It's also possible that the amount of visible blood affected the rating because it's mentioned in the rating summaries for both Halo Reach and 4, but is not mentioned in the summary for Halo 5.