I think I prefer the level design and layout of Demon's Souls over Dark Souls as well, and for most of the reasons you explained. A sprawling world is fine but these games have a lot of things to keep track of all at once and it's nice to just have a, more or less, direct path to have to follow, with shortcut rewards for branching exploration options. Being somewhat familiar with medieval architecture, I can also say that I greatly appreciate all of area 1. It's a bit grandiose and no places like that actually ever existed, but the general look and functionality of the various sections feel very well researched. It knows it's a video game but with the PS5's processing power, you almost feel like you're actually there.
The swamp area wasn't that rough, IMO. There was a point in the game where I basically became sort of OP, going with the Saint's garb, a Quality Winged Spear +4 (didn't get the Pure Clearstone for the +5 until very late) and the large purple shield with high fire resistance (can't remember the name right now). I had a super high Strength and Vitality with Herculean Strength ring early on so on top of everything else, so I was very mobile on top of everything else. I was one and two shotting almost everything by the time I gave area 5 a serious look. There was one black phantom with a greatsword down there on the fringes in the swamp area that iced me and I just never went back to her because once I unlocked the shortcut to the 5-2 boss, I never had a reason to. There were also a couple of areas where some of the larger club monsters (trolls, I guess) were a bit of a challenge but they were all avoidable and I had plenty of good equipment and ways to get souls so I felt the ROI on gathering those drops just didn't make sense. If I NG+ it, I may revisit them just to see what the goodies were. I killed Yurt immediately after freeing him because I know he's a complete cockass and I wanted his Gloom Armor. So before completing area 3, i went and dealt with area 5 wearing the Gloom Armor. Its resistances greatly helped while rolling around in the mud, but my dodges were so armadillo-like you could meme them. Spacing benefit=zero.
The Maneaters were an enemy I had to come back to, admittedly. They were wrecking me with their dash although eventually, I did manage to figure out the timing and roll through them. When I finally took them out, my Guard Break was so high that I could resist getting bowled over four times in a row. When I finally killed them, I was swinging the Blueblood Sword like I was born with it in my hand and doing MASSIVE damage two handed. Because I was able to fight in such a fashion where I didn't need to use the whole area, I was able to keep the second one from spawning right up until the first one was down to 25% health or so. With the increased confidence gained from being able to stand my ground rather than having to fight evasively, I could effectively circle the enemy with little fear of a bottomless pit death. I would get vertigo when one of them took to the air, flew around and then came roaring back in but that was also a good time to rush in and land some blows two handed. Overall, I'd say that the fight is one of the more difficult boss battles because of the precarious footing and having to kill two of them, but with some grinding and the right shield, it's not an impossible task. I'd say the most frustrating enemies to fight in all of 3 are those Mind Flayer jailer dudes. Don't know what they're called but any enemy that can spam attacks while you're impaling them on a spear, paralyze you and then do 3/4 damage is bullshit.
At the end of the game, I chose to let the Maiden in Black live and I got the Soul sword (the 'bad' one). Is there a way to get the other sword that Allant was buried with?
That last encounter inside the Old One is my favorite game ending boss fight of all time. It's the right kind of subversion, one that totally makes sense, is expertly applied AND doesn't insult the players/audience.