The stats you see for Assegai and Harimau are:
Code:
Assegai Harimau
Speed 8 8
Thrust 8 7
Handling 9 9
Shield 7 7
So it does look like Harimau is just a crap Assegai. However, these are just the simple displayed stats on the team select screen. It's entirely possible (in fact likely) that these are truncated, and the real stats aren't integers. I'd guess that Harimau have larger fractional components. For example, the table of stats could actually be:
Code:
Assegai Harimau
Speed 8.3 8.7
Thrust 8.2 7.6
Handling 9.5 9.1
Shield 7.3 7.9
(I'm not saying that they are these exact figures; I have no idea if Assegai has better handling than Harimau - this is just to demonstrate the point)
Those would be mathematically balanced and still result in the same stats you see displayed in the game, assuming those are truncated. However, I doubt the ship stats were created that simplistically; the developers seem to have put a lot of effort into balancing the different teams so I'd imagine the stats were decided upon after copious playtesting, and having an exactly matching total isn't going to give an exactly matching overall performance.
The short version: while the stats you see seem imbalanced, I don't think they are, and anyway the stats are only an indication of overall performance, not the generator of it.
The only way to establish team tiering is to do it like beat'em-up players do; set up an exhaustive series of 1v1 races, pitting every team against every other team with the best pilots you can find, and record the results. Wipeout is more complicated because the track used will greatly affect the outcomes, so you'd really have to run tournaments over all courses instead of single races (or run 8(/16?) seperate comparisons to find out what ships are better on what tracks). It's an awful lot of effort to go to, especially given that there doesn't seem to be an overpowered or underpowered team; at least, I've never seen anything posted about abuse or disgust. I was expecting Icaras to be the go-to team, since on paper it's the most broken, but that doesn't seem to have happened.