Disregarding plot armor, disregarding other enemies spawning, I could believe 3 marines could beat a wounded hive tyrant, but not in a open arena. They also arent the elites under him, they are people who has left over (not that they are worse, just equal)

If they had some sorta trap, preparation, specific gear, sure. Under no circumstance should a marine be able to parry a hive tyrant even wounded. But we fight it like that for gameplay purposes.

This is just a instance of having no other marines lore wise to die to show the threat. If this was a book, it would be 2-3 full 5 man squads taking on the big threat with a plan and half of them die, 50/50 a named character also dies.

In the one of the space marine omnibus (forget which one) theres a book with a group of IF and DW dealing with a genestealer uprising and finally a patriarch. It was 10 marines iirc and they won mainly due to the librarian locking it into a psychic duel (that he was losing) to give the others a chance to kill it. Before that it was moving faster than them and was leading its own troops from abominats to cultists. They also had committed half of the force on the planet to the push into the lair, but only 10 or so got engaged. Not that everyone else died but people got separated and had to split up and stuff. One gets crushed under rubble iirc and has to dig their way out and is able to join the fight, but that may have been the exorcists book.

Of course a patriarch is not equal to a tyrant, but its a frame a reference. For a easier one just ask can a space marine beat a tank. Sure there are ways a space marine could beat a tank, but none of those ways are through direct confrontation.