I just spent days rendering something in 2.80, and it's got some problems, so I'll need to re-render. The thing is I don't even need anything but OpenGL rendering for this, but OpenGL along with the ability to render with it seems gone from 2.80. EEVEE seems fast enough in the viewport, but when rendering to PNG files at 50% of 1920*1080, it has taken three or four seconds to render/save the image. Sometimes I've suspected it is re-working whatever preliminary work it does on the scene (IE: the delay when switching to rendered view that only happens on the initial switch) for every frame. I deeply miss OpenGL render. I'm not sure how to state this all as one question, unfortunately.
Technically, blender 2.8 has three render engines- cycles, eevee, and workbench. Switching the engine to workbench will render in the same way that opengl used to. And the reason that eevee renders slowly (or at least not instantly) is because it still takes multiple samples for a final render. It is only real time in the viewport because it takes a fewer number of samples. Adjusting settings in eevee can optimize it in the same way that adjusting cycles settings can optimize it. Also, a final render is going to be slower than a viewport render because it has to be saved/written as well, even though that might only take a few milliseconds.
This confused me for awhile. You can still get the viewport render, it is just not located where it used to be. Go To 3D Space > View and Select "Render Sequence Animation". It operates like the old OGL used to, and can be good for playblasts and what not.