The Hariri murder was just one of many.
As I recall, quite a few politicians, judges and what not got blown up.
The pattern seemed to be that all these were opponents of Hezbollah.
Yes, political murder is the national sport in Lebanon. That tradition, however, goes back at least 30 years, longer than Hezbollah exists. There has been factional strife as long as I can remember. Groups would (re)-ally with the murderers of their former leader the day after the funeral, in case you wonder why Hariri Jr. headed a government with Hezbollah. And he's lost more family members than just his father, IIRC.
It is already progress that the Hariri murder is investigated at all and that the UN report is there - none of the previous political murders were ever investigated, AFAIK. It would be a shame indeed if the report were not followed up.
That country is in some deep doodoo. There unity government depends on the support of a party that is financed by a foreign state and has a private militia that not only unilaterally declared war on a much stronger state, has now apparently assassinated the frigging prime minister.
They've never quite gotten out of the mess, it's always been a tight-rope walk. Lebanon was carved out of the Syrian mandate in 1923 or so by France to protect its interests there in the Christian community. The National Pact says the president must be a Maronite Christian and the PM a Sunni Muslim. Seat allocation in Parliament is along religious lines. However, today about 40% of the Lebanese population is Shia. Political parties have always been aligned along religious lines, and have also been used as vehicles for meddling from foreign countries, traditionally Israel and most importantly Syria - and with the rise of Hezbollah also Iran.
IMHO, the real underlying problem for Lebanon is that it never got rid of this religious factionalism. Religious differences are superficial. The real political differences between people are along class lines. (How's that for a left answer, Virus?

) Get rid of those backward religious divisions and you also largely get rid of foreign meddling, especially by a theocracy as Iran.