On a human level, we generally value being alive no matter the conditions, e.g., debilitating illness, chronic pain, etc., over not being alive. Of course there are exceptions like euthanasia, which are relatively rare. So why not apply that ethical equation to lab animals as well?
I'm just hypothesizing here. I don't particularly like animal testing, think its cruel, think it may be necessary, think it's a morally ambiguous situation, etc. Which is to say it's a complicated topic.
There's no experience of any kind related to not existing in the first place, so the two options are completely orthogonal. It's like asking whether you'd suffer from your parents never having met.
I agree with your first statement that not existing in the first place means that you don't have the capacity (or burden) to regret or cherish that existence.
The second statement is a little bit more nuanced, because assuming you derive happiness from your existence, and you already exist, you'd not have been able to experience the happiness if your parents didn't meet, therefore you'd suffer a net loss. I realie that there's a bit of circular logic in there of course, hence why I condition the assertion on the fact that you already do exist and therefore can make a judgement whether you'd prefer to exist or not.
Conflating the two makes one argue ethics from a realm of infinite possibilities instead of focusing on reality, which doesn't really make for great moral choices. For instance, should people have as much unprotected sex as possible, without any regard to their or their offspring's well-being, just to give the most children the chance to exist?
Most of us contribute much less to the body of human knowledge.
Does disabling Piezo1 have any side effects? I am guessing there is a reason for it. Might be more applicable in severe MS than aging.