Nothing wrong with a heavier arrow for many reasons. Although most tend to agree "Shot selection/placement" are paramount and #1 factor, many choose their setup based on some margin for error. Some prefer big expandables in case of gut hit, the theory being wider cut may kill the non-lung, non-heart, non-artery, non-liver hit faster and lend better chance to recovery.
I prefer to aim in a little tighter to the crease and err on side of "bone". This shot I never get tired of posting, because with my lighter arrows and dare a say an expandable like a rage, it's just not happening..
My 125gr VPA on the 470 total weight shaft severed the spinal chord, blew though all that bone, skewered the heart and was only stopped by ground.
I had something similar happen last year on a big doe early in the season. Shot placement was NOT "on" as things changed quick and at the last split second....
My wasp drone tipped black eagle rampage blew completely through the spine. At first while walking up, I thought it was just lodged inside. Well it wasnt. I found the front half of the arrow in the ground after the green started dying off about a month later. I was very impressed to say the least! Thats only 420 grains going about 270fps. Im not betting on that happening again by any means but confidence in my new setup was improved tenfold immediately.
Ive learned to believe that accuracy along with momentum are key in sending an arrow down range at a live target. I dont care much about the energy the arrow will have at impact. Because sometimes going lighter can increase KE but you will lose momentum. I want to know if I have enough momentum to blast through the tissue, bone or whatever upon impact of my target. Momentum imo is a bigger factor in penetration.