@John *********
now that's the big misconception here that I want to address.
Of course they are connected. Both are branches of the Thai government, both are involved with entry of foreigners into the country and yes OF COURSE embassies can see your travel history. It is actually the embassies, not immigrations, which is the primary body to determine entry eligibility. And a visa is nothing less than entry permission. De facto immigrations is handling most of the entry requests now, with the majority qualifying for exemption or for visa on arrival, but the default case of entering a foreign country is still that you go to that country's embassy and ask permission (i.e. apply for a visa).
Yes, it can still be overruled. Will it? No. That really isn't supposed to happen. I know excesses have occurred but a visa does more than only "improve" your chances; it means that you have permission to enter.