My perhaps naive observation is that the Mr Trump example has been responsible for Boris and Cummins adapting the barefaced lie approach more associated with Mr Putin than western governments.
The result is I question every statement from Downing Street wondering what sins of omission or spin it conceals.
Sad really that I have totally lost any respect for political figures and feel as though perhaps my admiration for individuals or even political parties of yesteryear was a con trick that today's leaders are indifferent to.
I agree with your first two paragraphs.
Regarding the third, I would say that this government is utterly different at its core than any others you may have admired in the past and you shouldn't question that too much.
In fact, when we all start going down the "they are all the same" route, it makes the election of people like Trump and Johnson much more likely. Fostering that attitude is what they rely on to be accepted.
The key is that post-Brexit political positions seem to have become so entrenched and polarised that like Republicans in the US, Johnson knows it doesn't matter if he lies, or gets caught lying.
It won't cost the party votes. No Tory voter is going to vote for Labour because Johnson keeps lying. 5 years ago UKIP would be a refuge for those people put off by it,15 years ago when we had a functioning Lib Dem party they could have been an option. Now its conservatives or a dysfunctional and incredibly weak Labour. No one is making that jump.
Worst case scenario is people disengage or don't vote which is still a net win for the tories.
When there is no consequence to lying then it becomes a very easy fix to all your political problems.