I don't really understand your point - but Afterpay certainly won't be competing in the +$2000 market, nor does it represent that it does. As I have previously stated, if someone is using Splitit to buy a $5000 pair of glasses, I imagine that pair doesn't turnover very often & is a high margin product. This is exactly Splitit's market, as I have also previously stated. If Glasses USA average order value is $500 however, I'm sure in time Afterpay would want to offer an option to Glasses USA - doesn't really matter that the first use of Afterpay wont be for a pair of +$500 glasses.
In this situation, the $5000 sale of glasses will likely return to Glasses USA approx. $4500 if they request upfront payment. If it is genuinely 'Split' then they will receive $4850 over the time period customer has Split (and pay interest on their payables I imagine?)