Had haglunds for about 30 years,,, grew to a golf ball size lump sticking out the back of my heel,,, ran with it but pain worsened over time until at age 53 nothing would touch it, icing , orthotics, nothing helped,,, I got to the point I could barely walk let alone run.
Had surgery with full detachment of achilles as the bone was huge, cast for 6 weeks non weight bearing,, boot after cast came off with gradual return to full weight bearing,,, I'm at week 9 and just beginning to walk in boot without crutches.
I'm really glad I enjoyed a full running career (since age 16),,, before I had surgery.
Listen, just like my surgeon told me there are no guarantees ,, I was lucky not to get an infection so far on the incision cuz that is a real risk.
Docs don't focus much on the potential complications and they are real.
If it's such that you can go with a lateral incision without messing with the achilles,, probably better,,, but better be prepared when dealing with surgical intervention of a large haglunds bump. There is no guarantee of being back to running in any certain amount of time.