yeah, i would sevrealy cut it back.
though, i think you dont want to cut more than 1/3 at a time anyway.
Does it get a lot of sun ?
some of my trees get a lot of sun on top, but the bottoms are in shade most of the day.
if that is the case, you might not want to cut it back that much.
hard to tell from a snapshot.
but, its certainly a good candidate to graft to.
my satsuma perked up after adding iron and epsom (magnesium)
but, thats all dependent on your soil.