That's certainly one way to paint the picture. Most of investing, though, is trying to grow the pie, not necessarily focusing on your specific piece.
I've been on the founder side (trying to convince investors to spin off a new company) and the pitch goes like this: Before, you had an ownership stake in 1 company with two products. After, you have an ownership stake in 2 companies. Both of these companies are out to grow, raise money and exit in their own right, and have teams solely devoted to hitting a home run. From that perspective, you could argue that you now own more than you did before, essentially by growing the pie.
I've been on the founder side (trying to convince investors to spin off a new company) and the pitch goes like this: Before, you had an ownership stake in 1 company with two products. After, you have an ownership stake in 2 companies. Both of these companies are out to grow, raise money and exit in their own right, and have teams solely devoted to hitting a home run. From that perspective, you could argue that you now own more than you did before, essentially by growing the pie.