And if you check which careers are the strongest two the result is two careers with unnatural traits (Psyker and Vindicare)
On the contrary if you check which two are the weakest its two without unnaturals. One clearly being the Stormtrooper. I'd say the second weakest depends on your playstyle.
certainly some individual pc can be weaker than usual despite being of a career that has unnatural trais but I'd say it's unlikely.
"Strongest" is a relative term also. From a numbers crunching perspective the Vindicare and Primaris "win". A lot of people like to forget the fact that both these classes are basically property and little more than tools to be used by their master.
Another question is how many GM's out there actually have and enforce strictures for any Death Cult Assassins in their group? They are part of a cult with a strict doctrine after all.
There are a lot of unwritten rules of who and what something is, including how they interact in the 40K verse, that people seem to forget. These societal rules are very important to keep in mind since they are what gives the other guys their time to shine. If an Inquisitor wheels out a Temple Assassin at a political meeting or social event the message is Death is Coming. An Inquisitorial Stormtrooper taken to the same event is going to send the message that I have power and the Stormtrooper is able to converse with people that the Inquisitor can't without raising suspicion, or causing people to run. A Temple Assassin is a death threat with a hand grenade after you pulled the pin, a Stormtrooper is a move on a regicide board.