It about the balancing act. Speed, pricing and capacity all matter. These drives allow HDDs to be more viable over a wider range of workloads; especially as capacities increase with HAMR. This is an important factor for the long term viability of HDD technology.
If you have all the money in the world, yes, SSDs are better; but if you have a budget (which everyone ultimately does) you will go for HDDs if they meet your performance and capacity requirements. This tech allows HDDs to deliver more performance per drive, making the tech more viable. This is especially true as we move to higher capacity drives.
Yeah, you can get a 30TB of server-grade SSD from the likes of Samsung, but how much does that SSD cost? How much is 30TB worth HDD cost by comparison?
HDDs will remain relevant so long as it delivers on price/capacity and can offer enough performance to meet the requirements of enterprise/server workloads. This tech will help on the performance side, and HAMR will deliver on the capacity side.