Not a fan of Thatcher (to put it mildly) but at least I get the impression she genuinely believed in her (flawed, IMO) political philosophy. Johnson appears to believe in nothing other than ego and power, and will do whatever it takes to massage the former and maintain the latter.
Also Thatcher knew when it was time to go and didn't stay on to fight the 1992 election against just about everyone's advice. Johnson appears not to.
Thatcher certainly knew what she was doing when she, and her acolytes, remember the support she got away from politicians, commenced their malicious actions under the guise of "Government ".
Boris however is different in this respect but, even more repulsive due to his well documented amoral lying narcissus nature, his total lack of credibility on the international stage, despite the fact he, and only he, thinks otherwise and the sheer arrogance that makes him feel he is beyond reproach.
Thatcher didn't go as quietly as you say....she had to be prised almost kicking and screaming out of office, and the front door, when eventually members of her own Cabinet finally had the moral courage to tell her she was being evicted. That image and shot in the car as she was driven away caused many to celebrate...including me.
We look forward to Carrie, who is as culpable as Boris in respect of his arrogance, slapping on the stage tears for her own departure. I should add, usually, politicians family members are immune from criticism relating to the politician....in Carries case, this is not applicable.