I don’t agree friend.
If you know, there is a sword called “Zweihänder” (two-hander) which originated in 15th century and gained popularity in 16th century Central Europe.
And it is not a longsword at all, because it is so heavy (up to 4 kg!) that you should use both hands mandatory and it is too hard to swing even then. Google it to see what I’m talking about 
Recently I visited Czech Republic and went to Konopiste castle… WOW, I was trully amazed from the medieval armory Habsburgs had collected through the ages. It was awesome experience and I had the opportunity to see in person all kinds of late-medieval to late-modern swords like nowhere else and compare them side-by-side.
And for the horse combat with a longsword, I think @warhorse should put it in. It is realistic and it is historically proven.
But anything bigger than a longsword in a no-no from horseback IMO