Hence why good designs are a combination of silhouette and COLOR (I mentioned that in the OP).
Like, superheroes OFTEN have the same silhouette, but are differentiated by COLOR.
Is this Superman? Supreme? Shazam? Hyperion? Sentry? Nomad? The answer depends on the color scheme of this character to help them stand out from other caped heroes. Is this a "nondescript, boring" hero design? Only if you remove every single other element that makes them unique - their colors, symbols, etc.
The same goes for Ironhide and Rachet.
You say them sharing elements makes them boring and interchangeable. Clearly they are capable of making different body shapes, so it's a conscious design choice. Why? Because they're created as the same "class" of Transformer in the original continuity (and also, yes, because their toys shared molds).
It's faithful to the original designs of the characters. You call it "generic robot", but Transformers is a huge reason we HAVE a mental short-hand for what a Transformer looks like. They look great, are easy to identify by color, and, yes, even shape (because the movie focuses on their faces so you can easily spot Ratchet's horns opposed to Ironhide's smoother dome).
I mean, they put the two of them literally side by side in the Bumblebee movie.
A combination of simple designs, striking colors, and good framing makes it easy to spot who is who, modernizing "boring" old designs (I NEVER felt they were boring, fwiw), and making sure they still stand out without being lost in the action, backgrounds, or among other Transformers.