As others have said, the different alt modes with
Slingshot^Alpha Bravo and
Wildrider^Off Road may be due to potential mould reuse for the Combaticons, but one added advantage - especially for the Aerialbots - is increased variety in the alt modes, which impacts on the look of the overall gestalts. One thing that particularly made the G1 Aerialbots dull as a set, was the generic nature of the limb robots. Although they all do have different alt modes as fighter jets, they all follow the same transformation pattern. And in both the G1 cartoon and comics, it often made the individual limb robots indistinguishable when they formed Superion. The same could sometimes happen with Menasor, especially the leg robots unless viewed from behind. Colour was often the only way that you could distinguish which robot was which, but in situations where we weren't able to see the colours, it became impossible to tell. Look at these examples from G1 canon and see if you can distinguish which Aerialbot was formed which limb...
Hate Plague infected Superion.
Superion vs Menasor in the US comics.
Superion in the UK comics.
Superion vs G.I. Joe
Superion being owned by Combaticons in the G1 manga.
As a helicopter and 4WD, Alpha Bravo and Off Road are more distinctive. That's one thing that made sets like the Combaticons and Protectobots so cool; each of them have clearly distinctive forms. You can look at a black and white illustration of say
Bruticus or Defensor and still tell who is who. :)