I think it does matter what other PMs have done, since this country has no written constitution and works on precedent.
With respect, I think you're very muddled here. Our constitution doesn't 'work on precedent'.
Our Common Law system (which is one of several of the sources of the constitution) is based on concept of precedent, however, it feels like you don't really understand what that means.
In simple terms, lower courts are bound by the prior decisions of higher courts. Therefore, if a higher court makes a ruling on an issue, and an identical case later comes below a lower court, they must follow it.
Notwithstanding that John Major and BoJo's actions were factually different, there was no legal challenge to Major's suspension. Without a legal challenge, there's no court case, no judgment and no legal precedent.
And that's ignoring the fact that last week's judgment was made by the highest court in the land, who are not bound by precedent anyway.