Alakazam outclasses Froslass as a lead. Faster Taunt, kills U-turned pokemon and Honchkrow/absol/Dugtrio switch ins with Counter, Encores attempts to setup, and hits back with a very powerful STAB Psychic.
To Froslass, he Taunts and 2HKOs with Psychic before she can do jack. Alakazam anti-lead prevents Rocks 100% of the time (alright, maybe Scarf Mespirit) and beats every lead with prediction.
Rhyperior, on the other hand, is extremely underwhelming. Despite his high attack, he can't neutrally OHKO much of anything in the tier. RP Set is outclassed by Torterra, SD set is outclassed by Absol and several others. He has potential as a defensive tank, but Donphan has slightly worse stats without the horrid 4x weaknesses Rock/Ground have AND Rapid Spin.
Tomb is great, though. I run a trick/band priority tomb with pursuit. Never had any trouble with Alakazam.
I didn't want to show this set yet, but you forced me to
Froslass @ focus sash
Naive; 252 Sp Atk/ 40 Atk/ 216 Spe
Spikes/ Blizzard/ Ice shard/ Shadow ball
-This lead set I made because almost everyone assumes ambipom beats froslass when in all actuality it will lose ~70% of the time if it has life orb. I figured froslass, ambipom, and alakazam would all be top leads and I wanted to be able to beat their standard builds. I know Im relying on bluffing taunt + destiny bond which actually hasn't been hard to do at all (think back to the crobat days when crobat didn't have to use taunt to make the opponent not use SR) and its a small price to pay to beat the leads that "counter" froslass.
*Note* I kept it with a + spe nature simply to outspeed missy as a secondary check for my team though it rarely lives that long anyway. It in no way needs this much speed if you have a missy counter already; it could easily be a rash nature with more ev's in attack for ice shard and work better. I'll have to test.
How it beats ambipom-
Blizzard -> Ice shard (if ambipom has LO, and I don't see why it wouldn't, it loses as long as blizzard hits. W/ silk scarf it will be at ~4%)
Ambipom will either
A) Pursuit/ Payback and fail to ko
B) Taunt and give me an extra chance to nail them with blizzard (I dont mind to set spikes later at all if I can kill and ambipom early)
How it beats other froslass-
They are faster, I know this and they dont.
They will either
A) taunt resulting in them dying before they lay any spikes
B) Shadowball resulting in them dying before they lay any spikes
C) Lay one layer of spikes which is all they will get
How it beats alakazam-
shadowball -> ice shard
Alakazam will-
A) Psychic in hopes to ko making it lose
B) Taunt expecting ice beam making it lose
C) Light Screen making it lose (though it does get a screen T-T)
Alakazam, like ambipom believes it has the upper hand when it's actually a free kill.
(Its a ko 100% on 252 Spe/ 252 Sp Atk/ 4 Hp alakazam with the above spread, but it they begin to run more bulk, then the froslass can just run the rash nature to beat it)
----------
About Spiritomb-
I would rather run a bulky one to help with gallade as well. Sucker punch always ko's 4 Hp/ 252 Sp Atk/ 252 Spe alakazam with no attack evs meaning pursuit will as well if it switches. Its much easier to trap this way. At the same time I run enough spe to outrun 8 spe rhyperior and WoW + pain split for gallade and rhyperior while still maintaining a decently powerful sucker punch. Ah spiritomb...