Opinions, opinions everywhere.
You are overestimating Gai and underestimating Kakashi that's why you can't see that they're equals. Fact is the 5th gate doesn't guarantee a defeat being that kid Gaara overcame it. You also can't just state that the 6th and 7th gate would defeat Kakashi because there is a high chance that he'd devise a plan to avoid being hit directly. Given Kakashi's keen intelligence and his diversionary tactics avoiding large scale attacks requires minimal effort.
Besides if you must open the 8th gate to beat someone, you might as well call it a lost seeing that you die afterwards. Now if you kill them with the 8th gate then it's a tie because then you would have effectively halted their actions as a shinobi completely, in exchange for your life of course.