As far as I know the academic consensus is that taking in more nicotine, even a lot more, doesn't turn vaping into something as harmful as smoking. Addiction is the main established "harm". Nicotine, even very much of it, is not considered a carcinogen. There are studies that suggest it could promote tumour growth but it hasn't been shown in humans. There is also decades of data from nicotine replacement therapy and Swedish snus users and it shows little to no increase in heart attacks or strokes in otherwise healthy people. Another risk is accute poisoning, i.e. swallowing large quantities of liquid by children. As far as I know even the more alarming voices regarding nicotine do not regard it as harmful as inhaling fumes from combustion.

Also I don't think that there are many people that overdose nicotine regularily because it causes nausea and dizziness so people are normally self-regulating the nicotine dose automatically. So the scenario you are proposing doesn't seem to be something we can actually observe as a common consumption pattern.

Too much nicotine is far closer to drinking too much coffee than to smoking and has similar acute effects which is why almost nobody does it on a regular basis.