Doesn’t make sense. None of it. Firstly — your business should make money. If you have millions/billions to data to process, of course you don’t need BigData solutions, you can use RDBMS for that kind of data. So you won’t be Google. You’ll be Oracle with all the expensive SQL warehousing solutions, because one of the benefits of Hadoop for example, is the ability to run statistics/aggregation/calculation on cheaper hardware.
Same goes to Kafka. You’re right. A lot of companies are not LinkedIn. But they still want a near real-time feature available for their product. So having a lot of data and RDBMS will never ever make near real-time possible. It’s not about becoming similar to big companies, it’s about solving problems with available tools. Which now could be achieved without using RDBMS