Seforno ad loc. explains that "Yitzchok was under the impression that he was speaking to Esau, he thought that it would be in Yaakov’s interest to endure some degree dependence upon Esau while at the same time holding on to the Land of Israel as its Abrahamitic heritage."
Yitzchok knew that the Land would belong to Yaakov exclusively, which also explains ...
Rav Menashe Klein in his Mishneh Halachos 11:182 and 18:143 writes that on a ruler one makes a bracha even if they do not have they power to kill someone. He notes that for the President one can make a bracha ,but a governor he is unsure ,since the governors of yesteryear had more power.
Text of the teshuva: