I feel exactly opposite. Notable skills in the tree make a huge difference to how the combat flows, even some "I'll grab them if I'll have spare points" skills that I was initially skeptical about, like throwing a discarded weapon at an enemy or missile reversal.
While stealth being optional is true, assassin tree still has a lot of notable skills that are very, very fun to use and nicely enhance the general playstyle.
Overall the combat is a huge improvement over ACO, mostly thanks to these passives and conditional skills. ACO was basically jus spamming attacks and parries until you built up adrenaline so you could Overpower or Hero strike your way to victory. Here I'm literally using all the tools at my disposal because the devs had this brilliant idea of allowing us to grab everything on the tree - normally I'd be soooo against something like this in an RPG but it works so fricking well here that I still can't believe it. Earlier I wrapped up the Essex arc storyline that concluded with a battle that lasted about 10 minutes, and I was dodging left and right, parrying, swapping my main and offhand weapons based on the enemy I was fighting, grabbing missiles midair and shooting them back, throwing weapons that were dropped by dead enemies, liberally switching between melee and ranged without feeling like I'm gimping myself, using abilities for both playstyles, managed some tougher elites with carefully timed CC (harpoon ability etc). It ended up being 10 minutes of some of the smoothest combat flow I've ever experienced in a game of this type, and just nonstop carnage and gory executions. I fucking loved it and cannot wait to get more. I'm actually playing for the fun of it and trying to go for some flashy moves instead of just worrying if I'm squeezing the maximum out of my character at every opportunity. Fuck that shit.
Fwiw I'm on highest difficulty, currently power level 318.
Valhalla is so far ahead of every other AC game in every way imaginable that it still blows my mind how good it is.