There's a giant difference between randomly hitting on the same melody as an existing massive hit AND then re-using that melody as the first hook in your own song. And Scrubs by TLC is a massive cross-generational hit that Sheeran can't claim not to know without making himself look like a tourist in the pop world.

Sheeran's lifting was so blatant I assumed he was intentionally quoting it. Doing that is fine - and it happens regularly, especially in rap and R&B - and is even encouraged when there is overlap in the publishing rights holders (label, publishing company) with the original writer. But royalties should and do follow. So I'm just baffled that he still thinks he is being taken advantage of here.

Fwiw, a much less fair copyright infringement case was the Tom Petty vs Sam Smith case around "Won't Back Down" and "Stay with Me." The musical similarity there was much smaller and there are likely scores of gospel songs that use a similar melody.