It didn't look like there were even 100 when they arrived however I think that the Klingons had about 600 to evenly match the Starfleet numbers. In the episode before sacrifice Dukat stated he was pulling enough ships to crush them so I think Dukat saw how many ships were headed that way and pulled double the amount for them.
It was just the Klingons and the Federation at this point in the series, the Romulans weren't involved as of yet. But it was also the the Jem Hedar and the Cardasians. In the Next Generation we saw that at least Galaxies were able to top any Cardasian ship and the manner of talk was that at least in some ways Starfleet had superior technology to them. In DS9 we see the Klingons constantly pounding the Cardasians as well which was one of the reasons Dukat got the Dominion involved in the first place. I don't think to many Jem Hedar ships were taken out but a whole bunch Cardasian ships were. It would be interesting to know the ratio of Spoon Head ships to Jem Hedar ships that were sent in.
Also, I don't know much with the term "flanking". But I guess there is more damage to be done to a ship if you were able to hit broadside as opposed to straight on. There is simply more to hit and strike at. It looked as though the Klingons came in on a different vector than the Feds. When the came in the dominion were already immersed with the Federation. Maybe the element of surprise along with there different vector was enough to fully turn the tide.