I have previously written on what I feel makes a game souls-like or not. I think Sekiro has a lot of the same feeling that Souls games do, being made by the same developer and having a world that reacts similarly to your actions, but I don’t think it’s a Souls-like game because the combat doesn’t emphasize the same skills. I think Sekiro is closer to Batman Arkham Asylum than the Souls games.
Demon’s Souls was a critical innovation in combat systems compared to other 3rd person action games because of a few key decisions: Slow player attack speed, uncancellable attacks, shared stamina across running/dodging/blocking/attacking, a realtime healing animation. Sekiro has 1 of these, realtime healing, which is the least essential. Instead, Sekiro has fast attacks, it lets you cancel them for a significant portion of the startup of the move, and it does not have a stamina system, only a guardbreak meter.
By themselves, these changes already move it outside of Souls-like and into the territory of other 3rd person action games, such as The Witcher, or Zelda, but Sekiro undermines all hope of playing in any way Souls-like with the introduction of 2 new mechanics: Deflect and Mikiri Counter. Deflect lets you drain the stance meter of enemies (their health), by blocking within a certain window of being hit. If you do this correctly, your block cannot be broken, even if your guard meter is completely full.
Some moves however are unblockable thrusts. These can be countered by timing a dodge input right when they hit you, triggering a paired animation where you step on their weapon, dealing some stance damage. Some unblockable attacks are not thrusts and need to be dodged as normal, but they’re the exception rather than the rule.
Together, these mechanics mean that almost every enemy in the game, especially all of the major bosses, can be defeated by simply standing in place, and timing the presses of 2 buttons. Attacking isn’t useless, as it will damage the enemy’s stance, and reduce the rate at which their stance recovers, but since attacks are fast, and you can cancel their startup into deflect or counter, this means you can easily fit them in without any risk between deflecting strings of attacks. This is why the combat feels like Batman Arkham Asylum, because that game is also about pressing buttons when your enemies do stuff to play uninterruptible paired animations.
You do have a lot of other options. There’s a massive number of items, shinobi tools, and other stuff, but all of those are worse than just deflecting and countering with some stray hits inbetween. Since these 2 options are so much more powerful than everything else, it gives the impression that everything else you might do besides them is stuff you do if you’re bad at timing the core mechanics. Some enemies have shields that need to be cleaved with the shinobi axe, but this is shallow lock-and-key gameplay, which makes it look even more like Batman Arkham Asylum’s enemies that need to be stunned or vaulted over before they can be attacked. You could avoid buying the mikiri counter, but I don’t think this is reflective of anyone’s play experience and I don’t think anyone would argue a game should be judged on the basis of ignoring one of the core defensive tools. It would be like judging Wonderful 101 based on a playthrough where you didn’t buy Unite Guts or Unite Spring.
Sekiro also doesn’t really match other Souls games in that it doesn’t have a bloodstain system, instead having you lose a percentage of currency sometimes when you die, much like dying in an MMO; it has more of an emphasis on story and cutscenes with a predetermined character instead of one you made yourself; it doesn’t have any RPG style leveling; and you can pause. I don’t think these factors are as important, especially not the presence or lack of a story, but they definitely don’t fit the mold.
I just don’t think Sekiro is really Souls-like in any of the ways that count and it deliberately undermined the core Souls gameplay to produce something more like Batman. If it came from a different developer, I don’t think the comparison would be made in the first place, it would just be another 3d action game, albeit with a connected world, NPCs you can walk away from, and checkpoints that reset enemies and healing.