Crikey, so many PC's dead from random encounters... I enjoy the occasional random encounter, and they don't have to all be pushovers, but your write-up makes the campaign seem... pretty random. I'm sure it's not, just the way it's presented. Most important question - are your players having fun?
Anyway, in our game (which @pukanui was playing in), we actually did have a few fights which as DM I'd say were potentially quite dangerous, but with a group of experienced and smart players, and the odd bit of good luck, none were fatal. For example in Death House the players avoided all side-trek opportunities to get themselves killed (there are many), and the shambling mound was killed very quickly due to good PC builds with good tactics and plain old good luck. Early on a large group of Ghouls could easily have been deadly, but my dice ran cold and I only got to kill an NPC ('follower' of a PC). Baby Lsyaga's hut is way over powered, but a PC got super-lucky and pulled the gem out, disabling it, before it got to kill everyone who couldn't get out of its ridiculously big reach (by this stage, everyone else was running away). Looking for the Saint's Bones, six vampire spawn was crazy hard, we only had 3 players but they had luck with Turn Undead and they had acquired help from Iznek and some town guards, so I only killed most of the guards before the PC's eventually won through (it was tough). The Amber temple, early on, was a potential meat-grinder, but devil's sight on a PC warlock, and some decent scouting etc from two, made it manageable. Overall, I took every opportunity I could to kill NPC's, in preference to killing PC's - one player in particular bore the brunt of this and enjoyed it a lot.
Overall, I killed plenty of NPC red-shirts, which was part of the 'theme' I was aiming for. I killed a few PC's, two in one fight where everyone ran away rather than fight to TPK, where I first gave Strahd the kind of allies and tactics that showed he was actually a credible threat. But yes, overall most of the fights in my game were quite manageable for my group, I didn't want to run a complete meat-grinder, I was looking for some interesting role-play, which we certainly got, and some opportunities for the PC's to be tested but not wiped out just because I could. By the time they got to the castle, they did feel it had been 'easier than expected', but I think they had selective memory - they remembered the easy fights, the ones where luck favoured them, the ones where Strahd got hammered easily and he didn't live up to expectation... but they didn't remember so much, or maybe even realise, the ones where if my dice fell slightly differently, or their tactics were not so sharp, just how easily things could have turned out differently.
Certainly I thought "cat and mouse" is a great way to approach the campaign as a DM - Strahd will play with his new arrivals as long as possible, but killing them all isn't really much fun for anyone... Once the PC's get to the Castle, the gloves should come off more, but overall it really depends on what you want to achieve - an endless supply of new PC's arriving doesn't really make much sense to me, and while some players might well enjoy a meat-grinder challenge not all do - in my game we lost two PC's (one player moved cities, one PC turned evil and joined Strahd) - by that stage, my plan was to use the vast cast of NPCs already introduced, to fill the ranks with replacements; for example the player whose character (willingly) turned evil, took over Rictavio/van Richten, made a character sheet based on that, and played him as his PC; if I needed it, I would have done the same with Ezmeralda (player creates a PC based on the NPC).