Okay yes this has an answer but the last answer just stated the differnaces in the two like stats im going to pick up on almost everything he has forgot, that means going in depth into competative play.
Great alround stats but the one that really stands out is a monster 135 Atk which is something to be scared of.
Its Hp is also good and can make up for the fact when you are not running evs in speed.
Its bulk between Def and Spdef are also something to be proud of and the one major thing it has over Hippowdon is it gets a 50% spdef boost from the sand meaning unlike Hippowdon it can take up to 3 Scalds from a politoed which is possibly the biggest counter to sand teams.
Its 61 base speed is respectable when you take into account its well over ballanced stats and the fact its a big rock dragon thing -__- (what is it? Dinosaur?).
But that speed lets it out speed lots of the slow pokemon which is actually very usefull, though its speed can be increased by running max speed or using a dragon dance set and even a scarf set, all of which will work extremely well.
It has a resistance to psychic which can provide good synergy in the team as well as many other resistances though a weakness including a 4x weakness to 3 of the most common moves in the Ou tier can provide a problem and requires skill to build a team around that.
Ok this is where Heracross missed lots of info and thats why it should be on the team?
Roles Tyranitar can pull off
Ok so Hippowdon doesnt have an outstanding offence so If you want a good offence Tyrnaitar is the way to go.
Just like Hippowdon it can set up rocks but that requires more bulk which it can utilize very well reaching 404 Hp with max hp and over 400 Spdef in sand, over 200 Def is not to bad either.
Unfortunatly it does not get roar like Hippowdon and its only Phazing move is dragon tail which is not reliable at taking substitute users out as well as not brilliant accuracy.
So a Spdef set will normally consist of Stealth rocks, pursuit, Stone edge, superpower.
It works extremely well and will screw your team over bad providing good coverage.
Though as i said it can very easyly use an offencive set in both pysichal and special. (Yes special, it has a decent spatk stat not as Heracross qouted Wasted 95 spatk stat and has one of the greatest special move pools in the Ou tier.
Access to the bolt beam combo and flamethrower is already providing great coverage and paired with pursuit it can pull off many kos.
Pursuit is another thing it has over Hippowdon it can trap choiced pokemon then hit them for 120 base power damage as they switch.
This is great for taking out pokemon like politoed trapped into ice beam while being scarfed.
But its by far best stat is its attack reaching 405.
It can pull off so many sets including choice scarf, band, dragon dance, revenge sweeper, trapper and a general tank.
Hippowdon can not pull all of these off.
So its stats do not compare as well to the pswedo legendery but it can provide many other rolls which will be mentioned later.
Its Def is great paired with its monster hp allowing it to wall better than many other pokemon.
Its movepool for the roles it can pull off are great but it can only utilize pysichal and status/phazing moves.
Unlike Tyranitar it will not suvive many special special effective hits but it does have less weaknesses and 1 typing does lose dual stab.
It gets stab earthquake which is possibly the most common move used out there or at least has been.
It also has much better bulk than Tyranitar as it has access to moves such as slack off and can use curse well unlike Tyranitar.
Roles it can pull off
Well theres erm Wall.
It just about ends there really.
But just because it cant pull off many roles dont underestimate its power.
Or at least its walling power, if you can set it up it can become very very hard to take down.
Its Def and atk are boosted by curse which is very common on Hippowdon, with that its attack will reach over 400 depending on the ev spread you run after one curse.
2 curse and you have not only a moster attack but a monster def making no unboosted pokemon be able to ohko it with a pysical move.
You also have a monster slow speed which isnt needed anyway.
But unlike Tyranitar it lacks spdef so another common move/ alternative move for Hippowdon is stockpile boosting both defensives by 1 stage Max 3 stage.
Slack off is its healing move and makes it extremely hard to take down.
It has access to toxic which is great for stalling especially with sand up.
But it can pull off one more role very well, and thats a phazer.
it alike Tyranitar can set rocks up and this guy has the bulk to roar away.
This is a great asset to the team as it will blow away pokemon that have used boosts, switch ins and it will give the classic rocks damage every time which really messess with the team.
If you do run a phazing set stockpile is the way to go as it bacomes the most annoying pokemon to ko with recovery, +3 and phazing moves.
Spikes also good synergy to add into your team as that will cause serious damage.
Ok now this is over i hope ive given you some well rounded points and ideas, but it never harms anyone to use the two pokemon on the same team, infact its rather common for sand teams nowerdays as it makes taking your wether starter out twice as hard.
But if you want a sweeper, Tyranitar is the way to go.
If you want a tank Tyranitar can pull off a good special tank but curse hippowdon with Ice fang and earthquake hits like a truck.
But a phazing pokemon is deffintly going to be Hippowdon.
And if you want a wall use hippowdon.
But it all depends on how they fit in your team.
Do you have a major problem with fighting pokemon? then dont use Tyranitar.
Major ice problem then dont use hippowdon, do ou see where im going.
Also it depends on your playing style, would you use Hippowdon in a hyper offencive team? or a Tyranitar in a Stall team (well maybe) but you can see where im going and it all depends on your team and playing style and wether it can supporrt your team or wether your team can support them.