Unfortunately, this is all indicative of a top down approach by eBay, one which isn't properly thought through.  

Under Simple Delivery, anyone who wishes to send a Large Letter sized packaged by Royal Mail is automatically charged a minimum of £2.74 by eBay, even though it only costs £2.70  direct through the Royal Mail Tracked 48. 

For items which are worth less than £20, there is no need to use Tracked 48.  Normal post is sufficient as they are still insured up to £20 by the Royal Mail and you can also receive proof of delivery from the QR code.  It is therefore pretty pointless spending £2.74 sending a Large Letter item worth just a few pounds by Tracked 48 when normal second class post is sufficient and only costs £1.55.  

It is fine eBay having Simple Delivery as an option for those who wish to use it, however it should be just an option.  Making it compulsory is not just interfering, it is disrespectful and patronising to those who have successfully bought and sold on eBay for many years.