Lab flesh reinforces the idea that animals exist for us to use. It doesn't challenge anyone to end using them. Its goal is to reduce suffering in one form of use, which is a welfare position, not a vegan one.
Veganism is deontic. It rejects animal use, regardless of whether the use is painful. It wants to end the root — the belief that animals are ours. Suffering is a symptom of that belief, sometimes severe, sometimes absent. Veganism is not built around the symptom. It is built around the root.
Notice what lab flesh doesn't touch. Not zoos. Not horse racing. Not dog racing. Not vivisection. Not riding. Not wool. Not breeding for show. Not any of the countless ways animals are used outside food. Lab flesh has no answer for any of it — because it isn't a stance against use. It is a stance against suffering inside one industry. That is a utilitarian position, not a vegan one.
We would not grow children brainless for paedophiles to use, even if the children felt no pain. We refuse it because the thought is wrong — they are not anyone's to use at all, suffering or not. The injustice is in the mind of the oppressor, not in the behaviour of the victim. Lab flesh asks the same of animals and keeps that thought intact.
The category "flesh" stays on the table. The animal stays a resource. The mindset stays exactly as it was. The only thing that changes is the equipment.
Veganism is a principle — that man has no right to exploit the creatures for his own ends — and no variation occurs. — Leslie Cross, 1951
A version of flesh that still depends on animal cells is a variation of use. Lab flesh and veganism are two different stances with two different goals. They are not compatible.