There are no silver bullets. Traditional S3, with the durability guarantees that S3 provides, has a latency trade-off because the data needs to be copied to additional availability zones before acknowledging the write. Once you collapse everything to a single availability zone (i.e. S3 Express One Zone), you have little reason not to use Kafka, which scales costs within a single AZ without a problem. At $0.16/GB, S3EOZ is about 7x more expensive than normal S3 ($0.023/GB) for fewer copies of the data/lower integrity guarantees, or about 60% more expensive than MSK or Kinesis Data Streams ($0.10/GB). If you write to a quorum of S3EOZ, then you're tripling your S3EOZ storage costs, to 0.16 * 3 = $0.48/GB. And this doesn't include the cost of compute!
Where's the value above just running Kafka within a single AZ, with no latency trade-off?