They can be relatively safer in multi-vehicle collisions (importantly, that remains the case whether you're comparing 3 vs 2.25 ton vehicles or, e.g. 2 vs 1.5 ton -- you're not objectively safer, but you are safer in the current metagame at the cost of killing more people who aren't you).

In single-vehicle collisions against approximately immovable objects (trees, barriers, etc) though, that mass is no longer an advantage, and if the crumple zone doesn't function as well because of the frame design in a larger vehicle then you'll be worse off.

It's probably also worth mentioning that heavier vehicles tend to be more susceptible to rollover. More importantly, traction scales sub-linearly with vehicle weight, so stopping distance, the ability to not slide off a curve, and whatnot all have reduced performance. That increase in the chance of an accident matters.

It might be the case that most accidents are completely unavoidable multi-vehicle collisions where one would want to optimize with a heavy, sturdy vehicle. That's a bit of a different argument from just pointing out that heavier vehicles suffer lower acceleration when colliding with lighter vehicles.