If tyranid warriors were on equal footing with space marines, it wouldn't make sense to even deploy marines to a tyranid warzone

I keep hearing this sentiment everywhere, be it 40kLore or the spacemarine game subreddit. But how does it even make sense for a basic tyranid warrior to beat a space marine with a 50/50 chance of success? There are untold millions of those bioforms out there, outnumbering the entirety of the space marines 10:1 as a conservative estimate. Any attempt to beat back a tyranid assault would just result in the deployed space marine company being wiped out in a matter of days if not hours, wasting precious manpower and geneseed.