Gladiator was an outstanding film, I loved it. It was loosely based, perhaps, on Commodus, but like you say, it was not intended to portray his reign as being accurate to anything.
I have not seen the sequel, but in the same way as the original was not intended to be an acurate portrayal of Commodus, I don't think this sequel should even be compared to the original. They look like two entirely different movies.
It seems they only share the same movie name based in the same time period, but one did not have the ridiculous special effects.