To me the amount of panko used seems on the high side, maybe reduce it a bit.
And like FF says, don't overwork the mince. Just apply minimal pressure to form a ball.
What I would do is to mix everything together with half the amount of panko and gradually add more till it feels right.
Or divide the batch in 3, one with half the panko, one with 3/4 and one with the full amount so you can compare properly?