For me not at all... until I played the game repeatedly and had enough experience to go through the game without difficultly ( even w/o the best weapons such as crissaegrim) then it does lose its fun somewhat....
Although the first time I played SOTN I wasn't a "hardcore" Castlevania so I will be brave enough to admit while I didn’t “struggle” with the game per say, I did die a few times.. (mainly out of carelessness especially with bosses like the Granfalloon and Galamoth where your kind of expected to take your time..) so I am not sure if the relative “fun = challenge” with the weapons could be down to the fact I sucked anyway at the time ( shameful as it was >.>..).
Even when I played a second time around and looked at guides that pointed me towards getting the crissaegrim, dracula’s tunic, and stuff, because I was still relatively new to the game, I did take them for granted.. for example I was bashing away with Galamoth wearing the topaz circlet and crissaegrim equipped, and while he wasn’t too hard, I did nearly die. I basically got too comfortable with this weapon and thought I could have easily curb-stomped him w/o having to worry about evading his strike patterns....
After I realised how much damage he was doing while I stayed in one corner slicing away, I had to quickly mist-form away to the upper right then gorge through a few Frankfurters before resuming the battle with due-caution for his moves..
Basically what I am tried to get at is I think to me experience with the game also has a part to play with removing the said “challenge/fun” more than anything really..the first time I was completely oblivious to these items and only slightly more experienced second time around ( which was like 1 year gap between plays btw.. ) where I "cheated" per say, and looked them up. Once I wised up and didn’t overlook certain weapons due to ignorance I realised what the best combo was (like using mormegill on Richter, ect)
from a newbie kind of standpoint and with obliviousness to the game itself as a whole, I still found I had to keep on my toes and not get too careless ( though with most enemies with the crissaegrim they were rather pathetic..) especially with some traps, badly placed spikes and dangerous terrain and things.. I donno if I would call it a challenge but a game as a whole I didnt get “bored” with it as I knew I had to still be somewhat prepared with the areas and how to deal with them. Only when I deal with these obstacles ad-nauseam did I feel this game was too easy.. ( which by then I had played the game too often anyway)..
for me they kind of feel like little small extras. ( not quite omake, as they are still technically part of the main game as a whole, however unless you know the castle like the back of your hand..., you’re likely to pass by the opportunities without a backward glance..) .. kind of like any rpg where you usually have a kind of side quest to obtain this uber- ultimate weapon that will cull through most enimies like they were origami figures, but even though they are reasonably accessible in SOTN, you wont know where to get them or how unless brush through the game in its entirety with a fine comb and work for them. ( or look up a guide, which if you want a true “challenge”, you wouldn’t do anyway ) . and even with rings of vardia you still have to finish the game at least once, which by then you kind of already know what the game will throw at you.
Repetitive play will naturally make the game easier also, as you kind of develop innate responses to how to deal with tasks at hand, so that challenge will be lessened by your experience also somewhat, and by then it would get boring anyway..
So basically try to put yourself in the mindset of a first time player ( maybe even new to the Castlevania game as a whole) who has no idea where or when to find /get these weapons, unless they are luckily and decided it’s a good idea to stay in the inverted castle’s library and level of schmoos, it’s unlikely that they are going to get a Crissaegrim first time ( unless they get really lucky or decide wearing Alucart gear is a good idea throughout the game..) so the game will still be somewhat of a challenge to them as whole, maybe not by the obstacles but kind of like the first Metroid, where exploration is the key to getting the best out of the game..
Basically I think the “freshness/uniqueness ” of a game keeps it fun/challenging, and as a whole SOTN is so good/unique (design wise as a whole, an all) that I would come back maybe a year or a few months down the line and pop it back in again, and still would have a good time even with crissaegrim, duplicator, ect, having been rusty on a few details to what to expect... mainly because of how many elements besides the best weapons make the game great....
Does that make sense??? ( sorry if the grammar sucks btw, wrote this all in a hurry..)