Yeah it seems like a kind of contradiction if you want this to be ecologically effective. You can't simultaneously have the phenotype severely impact reproductive success and be super effective in controlling the population.
Which is great for a risk-management standpoint: the modified genes will only spread through great human effort, there's no scenario where there's unintended side-effects and we can't stop the spread.
It's great actually. We just have to keep applying the 'treatment' in affected areas. Rather than having it spread uncontrollably.
You could, look up 'gene drive', which has also been discussed in that context.
A gene drive doesn't work if there's no chance to pass the gene(s) on through reproduction
You can if it only impacts reproductive success a few generations down the line.