The vial system makes the beginning much easier for newcomers compared to the flask system, as you can have the maximum amount right from the start. I had some issues in DS3 with reaching the next shortcut/bonfire before depleting the supply of handful flasks.
True, but on the other hand, newcomers are more likely to find themselves completely out of blood vials after facing a particularly difficult boss and have to resort to farming, which wasn't an issue with Estus.
Chalice dungeons were meant to be played while proceeding in the main game. Even the early ones posed a challenge, if you started them when you got access to the first after beating BSB. The later ones weren't unfairly difficult, more a test of patience, even the notorious Defiled one. Personally, I enjoyed their roguelikeness.
I believe the repetitive design of the CDs caused a lot of players to ignore them until the end of their playthrough. I can certainly imagine a lot of people trying them out soon after beating the BSB (since Gehrman recommends seeking out the Holy Chalice) and then realizing after going through a couple of layers just how samey they feel, and then thinking, "Well, I just save this until later/I'll just wait until I'm done with the main story," by which point they're incredibly overleveled for most of the dungeons yet still have to trudge through them to obtain the ritual materials in order to access the actually interesting dungeons.
And I would say there's a difference between encouraging player patience and awareness and merely inducing frustration because certain bosses can consistently one-shot the player when their health is arbitrarily halved.
To my knowledge, you can make a pretty OP Bloodtinge and Arcade builds with gems. The latter is the only trait that improves beyond level 50.
You can, but at least in the case of Arcane, it requires pretty heavy farming in the Chalice Dungeons. Arcane gems are near-worthless until you're near the end of the main game, or they may not even fit your weapon. An example to illustrate the latter: I made a pure Arcane character who used the threaded cane (best fit the roleplay). I quite literally didn't level up anything except ARC until I got that stat to level 70, so my regular damage was of course piss-poor. I was hoping instead to make use of Arcane scaling on my trick weapon by equipping an appropriate gem, but the first guaranteed Arcane gem you can get (Fire) is crescent-shaped ... and the threaded cane doesn't have any gem slots of that shape. I had to wait until I reached the poison pool at the bottom of Forbidden Woods - nearly halfway through the game - before I could pick up an Arcane gem that was actually usable for my weapon, and at that point, one gem at 10.5% doesn't make a whole lot of difference.
Beyond that, there are so different gem effects like poison (fast or slow), reduced stamina cost, etc. that are completely inferior to simply stacking damage increasing gems. Like, I remember putting three slow-poison gems on my Blade of Mercy to see if I could proc the poison and I still ended up killing enemies before the effect would even trigger, it was ridiculous. I don't think the upgrade systems in the Dark Souls games are without issue, but they certainly allowed for more interesting and more effective experimentation and roleplaying than in Bloodborne.