I have already mentioned that with other words at the end of my reply and in that case you will not have a speed 25 times higher, but maybe at most 4 times higher than a single HDD, i.e. twice higher than a single tape drive.
Maybe I misunderstood, but the initial posting mentioned a restoring operation from tapes that was slow and my point was that using HDDs is unlikely to make it faster. For a restoring operation the duration will be dominated by sequential transfers, not by seeking, so tape drives would be faster than HDDs, unless you use ridiculous resources, like in my example with a computer per HDD and with a network fast enough to aggregate the data from all computers.
If we are talking about general-purpose data storage on tapes, then obviously, what is frequently accessed should be on SSDs, because the average seek time for a file stored on tape will be between 1 minute and 2 minutes.
I suppose that there might exist applications where there exists a quantity of data so large that it would be too expensive to be stored on SSDs and with worst case latency requirements so severe that it cannot be stored on tapes, so you have to use HDDs. However, in some 40 years of using all kinds of computer systems in many companies, I have never encountered such an application. Everything I have seen could be better handled by a combination of SSDs and tapes, without any HDDs. The only problem with tapes is the prohibitive cost of drives, which limits their use to data sizes of at least 50 to 100 TB, unless long term storage reliability is more important than the cost.
Also, why on earth would you need 25 spare computers for 25 drives??? 25 drives fit into a single 4U chassi. A single operation and everything is done.
Seeking a file on a harddrive is about 7ms. Seeking 25 drives is also about 7ms. But will be quite the operation for a tape system.
You don't just "buy three more readers", you are likely making use of tape robots and fitting them into your infrastructure probably isn't an afternoon of work. And the whole cost benefit of tapes greatly rely on the fact that you don't have to. Which is also why the latency skyrocket. You still want to perform your backups of course, maybe doubly so because of any unforeseen secondary effects that whatever caused the restore process might lead to - which will compete with precious time.
I'd love to use tape, but the cost is prohibitive and you really want to verify your backups so for home use it is quite the hassle. In my opinion. But if I stumble on a great deal, sure! It'll be fun.