Taking a look at who Osiris are, they are an elite team of spartan IVs. And Spartan IVs arent exactly like Spartan IIs but upgraded ODSTs. From that, they could have made Osiris more believable as a team by showing struggle and development.
In Halo ODST, they were not introduced as upgraded and stimmed up marines but as actual troopers dropping feat first into hell. In their introduction, they dropped from the sky and the first thing that happens is everything goes wrong and they troopers were dying as you and others barely make it into the city. They were not introduced as dropping in the middle of a fight and clearing everything out but showing their basic everyday life in just one drop pod. Not to mention their team actually had problems with one another but still pulled through the end… And then die out through stories… Making them loved in the end.
In Halo Reach, you were Noble team, bunch of powerful Spartan IIs and IIIs. But they were not shown as an unbelievably unstoppable force but an actual team struggling into a fight. They shown that anything can happen in a fight with any death… And that they can struggle their way through as a team but end up united in the end… Why making them also adored.
Then in Halo Guardians, Osiris was introduced as Spartan IVs as an elite team. And first thing shown to them is them falling out of the sky without drop pods into the middle of a fight with ease snd destroys everything in their wake. Once thst was dealt, they were still shown in other scenes how good they were by chasing a falling pelican or going 4vEct on Sunion without help. They were shown without troubles in fights or any loss. Not to mention the fact that they had no team problems and thst they were pefectly united in and out. Thus, proving that they were not enjoyable characters and pretty boring to be in Halo 5. Whst they did was cool, but not believable even with the spartan abilities… Every scene they used it was to run besides the 3 seconds in the first scene.
The ODST team and Noble team were portayed as elite teams that still struggle through the fight with the mission or one another. Osiris was shown as an already united team that faced through every possibilities with ease. If 343i wants them to be more likable, they need to struggle and develope like characters on ODST and Reach.