The only thing I said that was wrong is on the maybe vs definitely. What you quoted says that it COULD have massive effects if used somewhere other than Avernus, not that it WILL, as it's uncertain how well LEF will adapt to a foreign environment - it might not grow well outside of a swamp, after all. It also doesn't mention that it is considered to be an Exterminatus level threat to the local biosphere, and I'd think that our Biologis would have mentioned that possibility if he thought it credible. IMO, the predictable lifecycle of the LEF indicates to me that it isn't likely that it would ever consume all life on the planet (and cities can be made LEF proof as well), and could also allow for a chance to exterminate it on worlds that aren't Deathworlds.
But the easiest way to resolve this rather than arguing back and forth is to just ask
@durin what the Biologis's actual opinion is. So let's just wait until he weighs in before we continue.