Those fin-tech companies almost certainly pay more than Amazon already. IIRC amazon has a cap of 275k for base pay, which means even if you're James Gosling that's the most you're getting, the rest has to come from RSUs which amazon also has a terrible vesting structure for. Amazon is regarded as a top-tier tech company, but their pay is not on par with any of the other companies (Google, FB, Uber, etc).
More tech presence is good, but I don't think big name companies are going to be too worried about their employees leaving to get paid less and have fewer benefits.