For now, It's still Ethereum. Because they had the first mover advantage. It probably won't be the case in the near future. There are quite a number of great contenders for the number one spot. Ethereum will have to go above and beyond to keep its position. I think open source is both a blessing and a curse. It just depends on where you look at it from like you mentioned above.
RE: Natively Scalable Blockchain Ecosystems Will Continue To Encroach On Ethereum's Market Share