That's not correct.
Of course if the tablet is not responding, there isn't much you can do apart from waiting for the battery to discharge and automatic powerdown to kick in.

Removing the battery abruptly forces the circuitry to undergo improper shutdown and while it's true that in general it _shouldn't_ be harmful, nevertheless it shortcuts all the intended powerdown paths. This can expose weakness both in the design and in the manufacturing.

So i still think it's better to avoid it if possible unless one is willing to deal with the customer service (assuming the warranty is still valid).

For testing sw that can lock the device i'd rather start beforehand a timed command that does "poweroff" after a reasonable period of time.

Unless you are testing a custom kernel/module, chanches are high that the poweroff command will not be prevented and you'll enjoy the drivers doing a proper shutdown of the peripherals.