Taking harm reduction measures in the meantime is absolutely not a waste of time. We cannot be so naive as to think that your suggestions will happen in the short term as each of them require radical changes to the political and social landscape that will take (have been taking) decades.
The ban on cattle is actually much more problematic than it appears. I didn't understand just how problematic until very recently. Our world relies on the animal parts that are "left over" in the butchering process, not to mention the single most prolific and effective source of fertilizer for all of the vegetables that we eat is animal waste and the only method to produce enough of it to feed everyone is genuinely large scale animal farming.
Nuclear doesn't really solve the problem. Yes the energy generation is carbon neutral, the material still has to be produced, refined and transported, which is also quite energy expensive, not to mention the messy matter of material disposal. Further, nuclear does put out a lot of energy, but the ability to output an entire countries energy requirements from 3 plants makes energy security worse, because you have fewer fallbacks in the case of power grid malfunction (CSIRO published a nuclear feasibility study for Australia recently which highlighted this as a major issue with nuclear power). Even if all that works out, it still takes ages to build a nuclear plant, by which point you could have filled the grid with renewable energy and storage and saved a lot of time and money while also meeting energy requirements and reducing cadbon output.