[TheCommonNoob]

For a promoted class that theoretically relies on a lot of combo play, Kensei's require way too many skill points to invest in.
(This also applies to a lot of other classes but I'm focused on Kensei for my argument).

Even if you're a destiny Duelist, you'll still have to make quite a few sacrifices while choosing your skillset to fit your already restricted playstyle.
All of Kensei's skills/passives together is 81 SP. On a destined non-human, no trait SP you have 50 SP to spend. (35 for non-destiny).

Out of those 50 SP, 13 SP goes towards often mandatory passives and skills, so you're left with 37 SP. (22 for non-destiny).

Now to proc those passives, you need to hit someone with the weapon skills associated but you also want to actually do damage when you hit someone with it.
So that's about 25 SP (Kagekiri, Toiken, Hirazuki, Raijinken, Sharenzan) spent towards your offensive skills to make sure they do good damage. Now you have 12 SP left.
(You don't even have enough as a non-destiny so you're already sacrificing something here, not even counting the other skills/passives).

Continuing on, Wazabane can live with 1 SP but it'd be really nice to have 5 SP in it for the bonus +10 Hit/Crit. So you have either 12 SP or 9 SP to divide amongst 10 really unique skills/passives.
(Sheathe Sword, Absolute Death, Absolute Fear, Absolute Pace, Sacred Art, Blade Barrier, Tekagen, Hidden Cut, Reflect Shots, Counter Edge).

Out of those 10, I would even argue that Sheathe Sword, Hidden Cut and Sacred Art are mandatory for Kensei to take.
However that concludes my example of a destiny Kensei having problems even with the extra SP. (It's way worse without destiny).

Firebird and Ghost also run into a similar problem with 67 SP total for Firebird and 74 SP total for Ghost.
Though they have a much less "mandatory" skill selection, they still have some like:

Firebird: Falcon Strike (5), Any Defensive Option (3), Roaring Falcon (3), Riser (1), Ignite Power (3), Magical Feathers (2), Plume Echo (Main Class Only, 1), Boon of Apus (1).
18 or 19 Total SP "mandatory" spending.
(Falcon Strike (one of the best offensive skills in the game), Defensive Option, Roaring Falcon and Riser for Boon of Apus to proc for feathers. Ignite power for good damage).

Ghost:  Ether Invitation (5), Scarlet Twister (5), Blood Spike (5), Wraithguard (Main Class Only, 3), Last Chance (2), Afflicted Spectre (2), Claret Call (1), Rising Game (5).
25 or 28 Total SP "mandatory" spending.
(Ether Invitation can be lower but that dramatically increases FP costs. Scarlet Twister and Bloodspike are too good to pass up. Then Wraithguard and the passives are what make Ghost, Ghost).

And now for example of another class and its promotions, a destiny Martial Artist can get just about everything they want from Martial Artist, Boxer and Monk.
A non-human Verglas (arguably one of the best reworked classes) without the Spiritual Fighter trait can get everything they need just from destiny SP.

Another good example would be the reworked Black Knight.
Even with only 35 SP, 36 SP (with the Mercenary Work trait) or 38 SP (as a human with the trait), you can get about everything you need to thrive with Black Knight being in the main class or sub class slots.
(Without even being restricted to a certain weapon archetype like Firebird or Kensei).

And as an extreme example, Rune Magician, actually one of the best classes in the game only needs 37 SP to be fully kitted out. Sure you "need" to main class it but, if you're going to be a Rune Magician you might as well have anyways. So any race with the Arcanic Study trait can just beyblade and let it rip.

To end off my rant though, please take a look over some slightly older classes and promotions and reduce the SP cost of some skills and/or passives (especially Kensei)! 
It's hard to be thematic when even destined, you aren't the master of your own craft.

[Lolzytripd]

preaching to the choir here, I'm of the opinion that hidden cuts, bullet barrier, sacred art should be come 1/2 passives (1 for the skill, 2 points to make it slottless)

[Autumn]

I believe that since it is a combo heavy class, similarly to Verglas its autohits could scale the same as they are now but have 3 ranks maximum to them, also Counter-edge and Sheath Sword don't need to have more than 1 rank. But Hidden Cut is fine as 5 ranks.

[K Peculier]

I would love to see Kensei get a rework similar to how Black Knight is in the future. One part of it would definitely be to cut down on having to spend so many skill points so I can definitely agree on this.

The other classes mentioned could also use a bit of this as well with 5/5 skills going to 3/3.

I miss seeing Kensei vs Black Knight duels that didn't end up with a flattened Onigan Yamcha in 3 rounds.

Also sheath sword/counter edge/hidden cut should be reworked to the point of letting you be a more calculating and slower paced Kensei that rewards mind-game play similar to Boxer geists. (Maybe as a passive skill like how Aquamancer has one to change up a playstyle.)

[Lolzytripd]

I believe that since it is a combo heavy class, similarly to Verglas its autohits could scale the same as they are now but have 3 ranks maximum to them, also Counter-edge and Sheath Sword don't need to have more than 1 rank. But Hidden Cut is fine as 5 ranks.

that's fine accomplishes the same goal either way. Theres just so many skills/passives that require a second 5 rank passive to do a thing.

[Snake]

Pretty good observation. I agree.

[Balor]

Having played Kensei to death for the better part of a year. To the point it was the ONLY thing I played consistently. The points here are concise and accurate. The issue with Kensei is the *mandatory* cost of the skills in terms of SP. Even Ghost has some room to play and you don't NEED everything, because there is variety.

But because Kensei is particular to it's niche and is NOT a utility class akin to ghost. It hurts.

There are also SP traps like Wazabane, which is counter intuitive to full invest in, since it's used mostly as a means to walk up, proc fleur, and finish with a kensei autohit. It's your combo starter or extender, but at max level it only gives 10 hit and crit. for 22 FP. You don't want to spend 22 FP when you essentially get the same amount of utility out of the skill with 1 point.

The same happens with rajinken and sharenzan. The swa would be nice, but KAKEGIRI and Hirazuki are mandatory skills for your class along with all the other utility passives and such you want to take or need to take.

A BK esque rework, granting the class more cost efficiency in terms of it's SP expenditure would improve it's QOL immensely for it's players.

[Poruku]

I disagree with a lot of your choices, especially needing to take things like the ghost spells which aren't even that good. You're limited by skill pool size anyway.

In the end you need to make some hard choices but I feel the issue with kensei is not so much putting in the points, but the clunkiness of its offensive skills, I.E. it's mostly stuff where you need melee range or line, overlapping with sidecut and generally other classes like BK having much more utility, flexibility and versatility in their options. Still, putting the max ranks at 3 would probably be warranted

Also you don't need both hirazuki and kagekiri, pick one