The assumption I work with is that mmr is a function of both fundamentals and meta. Fundamentals act as the floor, and meta as the ceiling. Team interactions make this all the more interesting - some examples:
A player with no understanding of the meta but good fundamentals can easily be directed by their team and have the same output as a high(mmr, meta) player. However, direction will not always be available and this will result in some losses.
A team full of players with high meta knowledge but low fundamentals will lose the fundamental game too hard and lose most matches. Also experience the "too many chefs in the kitchen" effect.
A team full of players with high fundamentals but poor meta knowledge will perform reasonably well, but be outshined by a more balanced team.
The team that won the largest DOTA championship 2 years in a row was clearly one that on balance had medium fundamentals (at a pro level), and outstanding meta.