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 why he did not include it in the blessing of Avraham that he thought to give to Eisav.
He gives two reasons why this would be better for Yaakov: this arrangement would allow Yaakov's descendants to ignore geo-politics, and "if Yaakov had to be subjected to foreign domination, it would be better for it to be subjected to the rule by his brother than by other nations which would treat it more cruelly."
(translation via Sefaria)