in a world if perfect people with perfect armylists where all the ohh-so-godly tactics the armchair generals think up work, yes there the orks have no chance.
but truth is that allmost all games (yes even or especially torunament ones) are lost because people make mistakes or do not know all there is to know. If you sit in your comfortable chair and have all the time of the world to critique on tactics post most things are clear.
in theory nids can do nothing against a landraider list without insane luck and venom cannons but even though I had neither I won the game with the nids in the deciding game of my countries national tournament. in theory he can "just" move away and have a field day firing at my army with his theoretically invincible land raiders. in reality he realized that he wouldnt be able to shoot me off the table and I'd be sitting conveniently on both objectives (big bugs on his, gaunts on mine) if he didnt bring the fight. ever tried to fight an uphil battle, gaining ground against tyranids with a good half of your points spent in practically useless tanks?
same torunament I had dark eldar charge 6 whyches into 5 tyranid warriors (who were backed up with stealer aura and featuring a peltora of lashwhips) in three different places at the same time. back at home in front of your pc everyone can comment that this isnt a smart move because the whyches basically have a few more attacks but both wound and hit worse and dont have a pretty save either against volume of attacks.
currently tournament play is done at roughly a felt 10% of the possible "power" that could exist in 40k while internetdom-armchair-general-ing is done at 20-25%. your normal friendly store games count in between 2-5% in my book.
I'm shure now many people (especially those theory-ists) will be outraged that I say even the whole knowledge of the online community combined only reaches 1/4 of the possibilities. It is the (not so) sad truth. There is much to still be written and thought about which most people will never get to even grasp and those that do have that knowledge usually not waste their time writing about it. the old goatboy articels (before the crowd flamed him to death for beeing a "powergamer"... may they eternally burn in hell for that as much could have come from this discussions) or some of fritz' stuff with the eldar and necrons are the tip of the iceberg.
mathhammer is prolly the only theoretical concept the community has delved into and mastered to some degree (at least those who care) but there are still many completely unexplored avenues of strategic concept that lay bare. some examples for those who are curious: local vs global superiority, application of power, psychology, deception, tempo, logistics. yeah thats where the other 3/4 lay and there also lies the solution for everyone who thinks the world ends with each new, creeped, overpowered dex