Actually there are no points of justification that Sun strong in Kundali is against the love marriage.For the love marriage strong connection of 5th and 7th house along with the 11th house required in form of Planetary or Nakshatrik connection. and in such cases Sun may or may not involved for.But as per my experience any connection of 7th house or 7th lord with Sun both for Love or arranged marriage , ultimately the marriage will not absolutely happy.But for all cases of marriage predictions other planetary positions are taken into consideration.