Slightly different concept my friend:
1) The robots in the Transformers are way smaller than a building, whereas, from what the description says, the mechs in this movie are the size of buildings.
2) The robots in Transformers are sentient beings; the mechs in Pacific Rim are described as being remotely and neurally controlled by pilots, much like in Gundam or Evangelion, which could create a very different relationship between the two.
To compare something like Transformers to Pacific Rim would be like, well, comparing Transformers to Gundam/Evangelion, with a little Godzilla thrown in. The only similarities between the two are that they're robots who fight other beings/robots. That's about it.
And it's your final statement that basically points out how they're practically the same as far as movie projects are concerned. The long and the short of it is that it's still a giant robot action movie. Additionally, Transformers is a well-established, popular franchise. It stood to generate more interest in giant robot stories than I would expect Pacific Rim to do and what have we really seen in that vein since '07? A couple of alien invasion flicks, the upcoming Real Steel movie (at an extreme stretch) and news about studios vying for the rights of Voltron.
Gundam? Evangelion? BattleTech? Maybe one day, but not because Pacific Rim suddenly sparks studio executives into saying, "I know! We need a giant robot movie!"

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