You were asking about how well the iPad held up to Pencil use:
There was an existing and current thread with answers that could have been helpful to you and that’s why I pointed it out. Since then, the moderators merged your thread with the existing one. The moderators work hard to reduce the amount of duplicate threads to improve the usefulness of the forums for everyone.
In answer to your original question, the iPad glass is very durable without a screen protector. There are artists that have over 1,000 hours of Apple Pencil use with no discernible wear and tear. It is always a good idea to clean your glass and Apple Pencil tip every couple of days. Some quick wipes with a soft clean microfiber cloth is all that’s needed. For more persistent dirty spots, just dampen a portion of the microfiber cloth with water only and use that first, followed up by a dry section of the microfiber cloth. This will keep things worry-free for you.
If you choose to use a screen protector, keep in mind that you will eventually see blemishes on the screen protector because nearly all of them are not as durable as the glass that Apple uses.
Hope this helps. Cheers.