Sorry, but yes, it is mandatory. Using the combined offset corrects not only your drive's offset, but also minor inaccuracies the mastering plant made when pressing the disc, so to say. So why do we correct these inaccuracies? Well, it's possible that different pressings of the same game have different factory write offsets, but are otherwise 100% identical. It'd be stupid to have duplicate entries for these, so we remove (i.e. correct) said factory write offset.
Don't worry, even though we "modify" it, the dump is still accurate, but more in a sense of how the disc was intended to be mastered if it wasn't for these inavoidable accuracies, and not how the disc actually came out of the mastering plant. I hope this makes sense to you
Besides, your dumps would be incompatible to all the other dumps in the DB. You wouldn't be able to match anyone's dumps, and neither could anyone match your dumps.