True but remember some attributes, such as speed are harder to store.
Maybe, but once the storing is done, the potential for combat power is very high.
Yes having access to Allomantic and Feruchemical power is a plus but these powers are weakened through the Law of Hemalurgic decay. To say it's out and out better than Allomancy and Ferchemy is a strech skill Mistborn and Ferchemists have bot fought Inquistors evenly.
Inquisitors yes, but Inquisitors are rather far short of the top end of hemalurgic power. They had all the allomantic powers, yes, but I don't think they're ever shown using any of the feruchemical powers except gold for health until Hero of Ages. Even in HoA, they never use the true potential of combining allomancy and feruchemy in the way Rashek did. Storing a feruchemical attribute in a metal and then burning that metal with allomancy multiplies the stored power by a HUGE factor, enough that the Lord Ruler was able to turn the normal 1-to-1 storage and return ratio into a positive gain big enough to reduce his age by about 1000 years nonstop indefinitely, and fully expected to be able to keep that up for a great deal longer. Yes, the individual allomantic and feruchemical powers would be substantially weaker, but nowhere near enough to counter the increase for having the combination and using it to its full potential.
Hemalurgic Thug = half strength natural Thug
Hemalurgic pewter feruchemist = half strength natural pewter feruchemist
Hemalurgist burning his own pewtermind = quintuple strength Thug and feruchemist put together
The Lord Ruler burning his own pewtermind = 10 times normal Thug and feruchemist put together
Yes, I'm just making up the numbers here, but you get the idea, and I actually think all of those numbers are rather low.
And then you get things like this (again, actual numbers drawn from thin air):
1) Hemalurgist's normal strength is 1.
2) Hemalurgist burns normal pewter, increasing strength to 2.
3) Hemalurgist stores strength in pewtermind, decreasing strength back to 1 and storing strength at 1. I remember EUOL stating that storing more than about 20% of your strength normally was hazardous because of how much you need just to stay alive, keep your heart pumping, etc. This is already 5 times that, and can be drawn back at that rate without spending any on compounding it.
4) Hemalurgist burns pewtermind, increasing strength by 5, to 6.
5) Hemalurgist stores strength in new pewtermind, decreasing strength back to 1 and storing strength at 5.
6) Hemalurgist burns pewtermind, increasing strength by 25, to 26.
7) etc.
Hemalurgist fights someone, taps or burns pewtermind to gain strength over 9000, and sends his opponent into orbit with a light tap from one pinky.
Rashek did stuff like this. It's how he stayed young for 1000 years, and how he killed entire armies of rebels all by himself. No one else even had the ability to do so until Hero of Ages when Ruin took over the Inquisitors and killed the Keepers, and even if Ruin had them try it, they didn't have the time to get much experience at it or build up truly impressive reserves. Yes, Rashek's allomancy and feruchemy was natural and therefore stronger, but that's why he's the one thing I said actually could beat a top end hemalurgist besides a top end Awakener who knows what's coming and is prepared for it. Yes, Rashek himself got beaten by a mere mistborn, but only because Vin was Preservation's chosen successor and therefore could draw on the mists for power. Without that quite unique advantage, which itself is not really part of the magic system in my opinion, she would have had no chance at all.
Breath itself is not a scarce resource, every human has it.
Every human has exactly one Breath. You need hundreds to do anything really significant, and tens of thousands to reach the system's potential. That is most definitely scarce.
Unlike Allomancy and Ferchemy the resource used can be called back (Unless used in a Lifeless.) and it can do more abstract things. At the Sixth heightening they can Awaken things in the sound of their voice like say, a mistcloak, wit the right amount of strength however this can be countered.
That power comes at the ninth heightening.
At the Eighth Heightining they can awakenn metal and stone provided they know the commands, this screw over Feruchemists and Steel Inquistors. Although, awakening metal and stone takes a lot of Breath.
This is also a ninth heightening power. You need to convince 20000 people to willingly give you their Breath in order to get to that point, and that's not easy no matter how you look at it. Sure, you can reduce that number by getting people who have multiple Breaths themselves to give theirs to you, but anyone who's gathered a significant number of Breaths is going to be a LOT harder to convince.
As for winning through number of Lifeless, it appers you've forgotten the koloss.
True, though that's another point in favor of top end hemalurgists beating everyone.