When wood-like structures first evolved there were no bacteria that could penetrate the tough cellulose. The trees would just fall over and ... stay there, as rotting wood is just wood being eaten by bacteria. This is where coal comes from.
I suppose something along those lines could happen: Venusian microbes are sufficiently alien that Earth-based life can't really interact with them, while the Venusian can interact with Earth-based life, or something like that. They can eat you but you can't eat them.
In lots of sci-fi like Star Trek all aliens have DNA and you can create Vulcan-Human hybrids and whatnot, and while e.g. Star Trek does offer an explanation for this[1] in reality alien life would be foundationally different. It will have some sort of DNA-like encoding structure, which isn't DNA.
I agree it's somewhat unlikely, but it's also completely uncharted all-bets-are-off territory. It's not so much about competing, but more about how it will interact (or not).
I suppose something along those lines could happen: Venusian microbes are sufficiently alien that Earth-based life can't really interact with them, while the Venusian can interact with Earth-based life, or something like that. They can eat you but you can't eat them.
In lots of sci-fi like Star Trek all aliens have DNA and you can create Vulcan-Human hybrids and whatnot, and while e.g. Star Trek does offer an explanation for this[1] in reality alien life would be foundationally different. It will have some sort of DNA-like encoding structure, which isn't DNA.
I agree it's somewhat unlikely, but it's also completely uncharted all-bets-are-off territory. It's not so much about competing, but more about how it will interact (or not).
[1]: https://i.redd.it/16xmtid83sbf1.jpeg