As Ricky points out Van Gelder took into account the equipment being used at that time. Nearly all consumers had realatively poor turntables and cartridges that would almost certainly have problems tracking what was on the master tape if cut like that and the rest of their chain could almost certainly not reproduce it in any case.
According to Joe Harley many of the master tapes are still in suprisingly good condition, especially those on one tape type Van Gelder used. From listening to these, and he has listened to many. He says Van Gelder rolled off the bass and very high frequencies to allow for the equipment of the time when cutting the masters for release. I am pretty sure given his known diligence Van Gelder would have tested this theory out before doing this. I note what you say about noise reduction, but if Joe Harley is reproducing what is on the master tape then any increased hiss should be apparent. They don't seem in anyway excessive to me in this respect.
I also note your preference for originals, I don't have any Blue Notes originals (and way to expensive to buy now) just some early pressings that may be in a very few cases from the original metal work. I agree Originals in most cases are excellent and that may be, despite what I said above about the quality of the tapes, at least partially due to their 'freshness' when the metal work was made or it may just be a preference. When I have compared the few of the early pressings or in the case of Impulse where I do have a few originals I find it can go either way. I did note previously that I thought some of Kevin Gray's cut seemed a bit 'bright' to me, but that may be because I have become so used to what I expect to hear.
I think it may just come down whether we think the original LP's are an historically important document in themselves in representing the artists Music as most heard it at the time and since (and many do) or agree with Harley's opinion and approach that also has its supporters. I assume he thinks that better represents what the musicians were trying to convey. I often find myself caught between the two.