Sentinels have had a strong presence in NA although after Reykjavik they showed signs of decline. They are not having the same mentality as other top teams and had poor results follow them. Sentinels tried a coach which failed and this shows that they need to adapt to other formal signs.
The Guard boot camped together for 3 months together practicing and putting competitive as their highest priority. They put the mindset needed to win games and it gave them results throughout. Sentinels did not have any sort of cohesion in this way and have little chemistry in their matches.
I believe that Sentinels will have to put competitive play above streaming and boot camp together and start putting their all into competitive rather than a side hobby. I think they should make a roster change as well building around Shazam and Dapr.
TLDR: Sentinels failed to put the mindset towards competitive while Guard boot camped for 3 months.