Of course a spammer could try to include one sentence with a very close embedding for each query they want to rank for, but this would require combinatorially more effort than keyword stuffing where including two keywords also covers queries including both together.
The latter point you pick up on was indeed my point, that you can tweak your SEO spam to give you the embeddings you want to rank for. This actually isn't that difficult given you can run embedding models like SBERT in reverse adversairly to generate text that gives you the best embedding that you want to target (similar to adversarial attacks in image models where you can make a picture of the most zebra like zebra, see the work of Ilia Shumailov former oxford now google deepmind). This is rather cheap and more importantly far far easier to game that ranking high on google where the cost function is unknown. If using an off the shelf embedding like SBERT then the attacker here has the cost function known, and can optimise for it.
The talent displayed here is immense. I challenge you to do better.
This type of attitude is not constructive however, as if we followed this logic, we would not have coaches and athletes, as the coaches likely cannot do better than the athletes, but that does not mean they are useless.