It¡s always the cover-up that causes the real trouble. With pretty all the scandals that have wrecked politicians they could likely enough been able to talk their ways out of it if they hadn't denied the facts and attempted to cover things up.

With this current stuff, if Boris had been open about it, admitted there's been significant cockups, and he'd been careless about it, he'd have been in a far far better position now.
The clear evidence that he deliberately lied to parliament is probably the bit that most threatens his survival now.

When it comes to his playing fast and looses with the rules and so fast they can and do drum up all kinds of rationales and excuses - no one is perfect, isn't this trivial set against big issues like war in Ukraine, other leaders like Churchill or Kennedy or Lincoln had some deep flaws et etc. If he'd not muddied up things with the denials and the lies those kind of notions would have been far easier to sell.