No doubt a bonded bullet is better at holding together in a tough target, I think everyone agrees with that. Question is, are they needed for deer, and that is debatable. Millions of deer have been killed with regular cup and core bullets, as well as cast. Deer are soft and not very thick, at least around here.
Basically what the article I linked to stated, and something I totally agree with. Members of the deer family, black bear and Humans are much different than Elephants, Grizzlies and Water Buffalo. The venerable 30/30 has much less velocity than most .300 Mags. Using any bullet at a velocity and on an animal, it is not intended for, will give poor terminal performance. Using the most expensive bullet available is not going to make a difference between a clean kill and a lost animal if one makes a poor hit, or used on animals and/or at velocities it is not designed for. I've killed a lot of deer in my life, both with firearms and with bow, and butchered most of them myself. Very few bones in a whitetail that would separate a quality cup and core bullet, used at the velocity intended, other than the pelvis. If you need a bullet to penetrate the pelvis without separation, you need to rethink your shooting proficiency and shot selection.
Most folks have a idea of what works well for them and they continue to use it because of that. Confidence in your equipment, makes for a confident hunter. It does not make them infallible. It also does not make something else not as good or better. Never fails, every hunting season, I hear a story from a hunter that shot and did not retrieve a deer, that claims they "double lunged it" and the bullet or broadhead failed. They now consider that terminal projectile "junk". could never figure out, when they did not retrieve the animal, they know for sure the "double lunged it" and the projectile failed.....and not their shot. Most hunting type bullets intended for deer size game have been designed for both penetration and expansion. Both are important for quick and clean kills. IMHO, any hunting type bullet, made by a reputable manufacturer, used as intended, will perform just fine on deer size game, regardless of cost and construction. Difference in how well they perform terminally, will never be recognized by the average hunter, nor will it make any measurable difference in the distance traveled after the shot. Still, folks should use what they have confidence in and are proficient with. That
WILL make a difference. I hunt deer with handguns or handgun caliber carbines anymore. I use both Nosler/Hornady/Speer cup and core type bullets and Speer Deep Curl bonded type bullets. I have seen little or no difference in performance on deer, even when shoulder bone is hit. This is very obvious when butchering the animal taken.