No, here's what's more likely to happen.
You deep-strike on top of my fire warriors, and kill three or four and then charge them. And now, you are in the center of my army. Everything is within six inches of that unit. Storm of Fire lasts during your turn. Now you are getting hit by 80+ pulse rifle shots, whatever my pathfinders are armed with if they're nearby, whatever my crisis suits are armed with if they're nearby, and my vehicles get to fire overwatch if I put a Point Defense Targeting Relay on them. Oh yeah, and the Broadsides, with their twin-linked weapons. And markerlights work in overwatch now. And my Riptide gets to fire whatever he's armed with, if it's the Heavy Burst Cannon you're screwed, if it's the Ion Accelerator and it hits you're more so. If I had Longstrike, he might hit with his main weapon, either a Railgun or an Ion Cannon. It's dead. Now, the other one takes some damage from the overwatch, but probably doesn't die, and slaughter the Fire Warriors like the Tau they are. Now it's my shooting phase. It's dead. And now I direct the other two-thirds of my army, the anti-infantry bits, back to killing the Gaunts, and in all likelihood, using Zephyr's Grace to run as far away as I can while still shooting, ineffective or no, which is again assisted by markerlights being able to boost snap-shots. Or, another possibility, I counter your monstrous creature and substitute my own! Now I charge in my Riptide. It gets five wounds, can have Feel No Pain, a 5+ Invul save normally, can boost it to a 3+, and is considered a Monstrous Creature. It, too, has Strength 6 and Toughness 6. Did I mention it can take two drones for ablative wounds? Or that it shot at you before it charged, whether or not it's still Tau and has WS of 2 and three base attacks? Because now your big guy is stuck dealing with him. Meanwhile, I'm shooting the rest of your army, and by the time you finish him off, I'm ready to focus the heavy weapons on you.
Tau are one of the best armies for ignoring cover by the way, and my stealth suits have the same rules. Unfortunately, those night fighting rules don't exist anymore in that way, now it's just cover saves. And if it wasn't, Blacksun Filters give us Night Vision. And then I can put Interceptor on my Broadsides and/or Riptide. Especially the Riptide. Why? Because Large Blast Str 8 AP 2 hates everything, that's why. So does Heavy 12 Str 6 Ap 4 Rending. Even if it has Gets Hot.
Now let me tell you about the Tau's options.
First, the mostly-deepstrike list. The new supplement, the Farsight one, allows us to take Crisis suits as troops.
Crisis suits. As troops. And then Stealth suits or Riptides as my Elites. Use my Heavy Support choices and if I really want to, a Fire Warrior firebase to keep a presence on the Board. Outflank with my pathfinders and/or infiltrate my Stealth Suits with Homing Relays. Now my Crisis suits anything can deep strike within six inches of them, no scatter. So now you have Hammerheads and Broadsides and Sniper Drones and other ludicrous range heavy hitters hitting you with stuff from the other side of the board, while a bunch of suits playing keep-away with you shred your backfield.
On that note, of playing keep-away, the Tau are the worst army in Assault. We are, however, the best army at preventing you from getting there, barring certain ways to play Eldar. Case in point, give my Hammerhead Sensor Spines, you now cannot reach it, because it is on impassable terrain that it's skimmer base can fit on. Nothing else can fit there with it. So you have to shoot it. And it has a 4+ cover save from the Disruption Pods and the fact that either a. I move it half an inch back and half an inch forward, thus satisfying the requirements for Jink or b. we agree that impassable terrain gives cover equivalent to area terrain. Our suits can do it too, constantly, in the middle of your army. They have to make Dangerous terrain tests, but that's a 1 in 18 chance at best to deal one wound, and they have two.
Finally, lets get down to the real reason the Tau slaughter Tyranids.
All Sniper Rifles. All the time. My kroot, for a measly one point each, kicking them up to seven points a model, can now all fire sniper rounds. 24 inch, Heavy 1, Snipery goodness. Twenty in a squad. Maybe Krootox, too, for the giggles. And now? That Mawloc you're so proud of? Wounded on a 4+. Ignore it's armor save on a 6. And I don't just have one kroot squad, oh no, I have two or three, maybe. And they have markerlights so they're at BS 5. Kroot are truly amazing, especially since they have Stealth in forests, and move through cover. Hey look it's ironbark! 2+ cover save, thank you.
Then there's Sniper Drones. 48 inch range rapid fire sniper rifles that are buffed by Storm of Fire. Already at BS 5. And with Stealth. Stick 'em high up, in ruins, put an Ethereal on them to benefit from Majority Toughness 4 and Stealth, and 27 BS 5 Sniper shots go out at 24". Plus, the Marksmen can add markerlights on. So other units can kill stuff.
The trick to killing Tau is to assault. You cannot out-shoot them. Three Strength 9 shots, possibly four, for nine points, is simply ridiculous for killing infantry. A suicide suit kills tanks. Railguns excel at beating up MCs.
I know Tyranids have more than 'rush em', but their tactics usually devolve into it, and a swarm army of 'Gaunts, Warriors, and 'Stealers, is primarily a 'rush em' army.
So, for what I can do, I can flood the board with battlesuits, having enough that I can use them as meatshields and tar-pits if I want(the equivalent of six space marines worth for 66 points is pretty good...), I can go all Mech and have everything mobile enough to run away from you, then when you finally think you have me cornered, jump on top of the building and flat out for the objectives(HAHAHA Tyranids can't flat out!), my personal favorite is pulse rifle spam, in which I have 72 Fire Warriors in marching formation, with pathfinders giving ML support, Piranhas forming mobile cover, and crisis suits dealing with enemy armor. Hey look 216 Strength 5 Shots. Most at BS 5. Did I mention Leadership 10 and the ability to get Feel No Pain, Stubborn, or Run and shoot? Perhaps the Supporting Fire would interest you? Or maybe the possibility of fielding, instead, my own swarm of 120 Kroot and 60 Hounds? Perhaps I will outflank them. All of them. They get Acute Senses, after all.
I don't really have options for melee, as such, but Kroot can work as a buffer(their weapons are AP 5 and they have WS 4, even if they're only one attack each. Kroot hounds have two, and are cheaper. Plus, they have initiative five), and my suits/Vespids can get/have Hit & Run. Initiative 4 Drones and 5 Vespid helps.
Melee Tau aren't a thing, though...