I found - so far - a 8 streak for men and a 7 for woman in the Summer games. The Winter games produce way lower streak possibilities, since winter sports are traditionally limited to countries with low temperatures
top candidates at the moment (disciplines have referees, but not a judging system) are:
tennis, doubles, men: 8 (92-21); source
For Summer Olympics the event that screams out for variability is a Cycling Road Race, lots of competitors from approx. 60 countries, one round, lots that can go wrong. It was the first event I looked at and having trawled through all sorts of other sports and disciplines, the Men's individual road race has the longest streak I can find.
Not even close - Slater is still short by five whole titles.
Phil Taylor is a British darts player, retiring from pro competition in 2018 after losing what was his twenty-first singles world championship final, having won sixteen of them already.
This alone should suffice to justify Taylor holding a position higher than Slater. This Wikipedia list provides ...