The correct sentence would be: "John has more than 70% of the winning/the artwork/the award." In this context, "of" is the appropriate preposition to use when indicating possession or a share of something. The other sentence, "John has more than 70% portion to the winning/the artwork/the award," is not natural or grammatically correct. Regarding the situation you described, it would be more appropriate to say, "John contributed more than 70% to the team's winning/the artwork/the award" or "John is responsible for more than 70% of the team's winning/the artwork/the award." "She is the rock of the team." This sentence is correct and means that she is a dependable and supportive person within the team, someone the team relies on. "They are rocks of the team." This sentence is also correct and implies that there are multiple individuals in the team who are dependable and supportive, much like the first sentence. It's just referring to more than one person in this case. These expressions are idiomatic and are commonly used to describe people who provide stability, support, or are reliable in a group or team context.