For the 67s, the starting and continuous tractive effort with 125mph gearing are quite low compared with other classes.
Yes, that's my take on it too.
The high speed gearing on the 67 also means the maximum continuous TE is at a much higher speed than e.g. a 66 (92 kN at 75 km/h versus 260 kN at 25.6 km/h, according to Wikipedia) - this is important on somewhere like the Lickey, if climbing from a standing start.
At the 'heavy' end of the table, I suspect a solo 59, 60, 66 and 70 all having basically the same rating (1045-1075 tonnes) might have more to do with coupler strength limitations than anything else e.g. a 66 with a 66 banker is rated at 2400t whereas a single 66 is 1070t.
As for comparisons with the Stadler 'UKlight' loco family (68, 88, 93), this TE comparison graph from
Rail Engineer is useful, as it has 37, 66, 91, 93, and 2 x HST power cars on it. I would expect the 68, 88 and 93 to have very similar lower/mid speed tractive effort as they all appear to use the same/very similar bogies, ABB traction motors and traction drives. Incidentally, note the very low TE for the 2 x HST power cars.