The consequence is that it’s completely useless when youre grouped up which is most of the run. Essentially giving up Team Benefits for personal gain, hence you need to be really good/smart with it. The true downside is that people are more willing to call you garbage if youre garbage with loner.
If anything, we should be able to see team builds mid game like how V2 lets us. The best players are usually the nicest and would also give an advice or two to willing ears.