Is it permissible to rinse the mouth with water and complete the ablution after spitting out what comes out after rinsing the mouth during ablution?

What you are doing—the excessive spitting and mouth washing during ablution—is not legislated. Rather, it is sufficient for you to perfect rinsing the mouth (madmadah), with the desirability of doing so extensively for anyone who is not fasting. There is no harm in the ablution water entering the mouth or being swallowed. Your persistence in this matter may lead to obsessive thoughts (waswas).