You're assuming that Heimdall is acting solely as a glorified doorman but he's so much more.
Certainly he controls access to the Bifrost but his principal role is guardian of Asgard.
This is because he can see and hear practically across the universe to detect potential threats to Asgard. Essentially, he's the main guardian and watchman for Asgard
Heimdall possesses extraordinarily acute superhuman senses, most notably his vision and hearing. His senses are said to be so acute that he could hear sap running through trees, and "the tiniest plant growing in the heart of the hidden hills and see and hear anything occurring in Asgard or on Earth. Heimdall can also "look across time, as well as space", in one instance seeing the far-off approach of an invading party and correctly predicting that they were still a full two days away from Asgard; this ability to see what has yet to come is retained even after the establishment of the new Asgard on Earth.
Heimdall has been said to be capable of detecting the fluttering of a butterfly's wings "a thousand worlds away". Heimdall is able to sense the life essences of Asgardian gods throughout the Nine Worlds of Asgard, and has the ability to focus on certain sensory information or block it out of his consciousness as he chooses, being so alert that he requires no sleep at all. According to Ares in his War Plan for the Siege of Asgard, Heimdall can "see and hear as far as creation", even capable of seeing the Dark Avengers at Avengers Tower from Broxton.