When creating a basic track, the only effects I see offered are these weak, tin sounding selections that are horrible.
Have you tried the settings In the Basic GarageBand installation without JamPacks I do not see any settings at all for the "Basic Track". Have you tried to use an "Acoustic Guitar Track" instead? The four presets do not sound weak and tinny at all with my acoustic guitar.
Maybe this is caused by recording through the internal microphone. Its characteristics are better for speech signals than for music. Do you have a strong enough signal, if you do not add any effects? What does the signal look like in the track editor pane?
If you want more strong effects, you might consider to copy your acoustic guitar recordings to an electric guitar track. Some of the amplifiers and stomp boxes, like "Clean Combo" or "Classic Blues" do sound good with an acoustic guitar.
I was able to work with some of the settings in another panel to achieve a satisfying result. The old GarageBand version allowed the user to select an acoustic guitar setting and begin playing. The current version requires the user to edit the acoustic guitar setting by accessing an additional panel and from there, select from a plethora of settings. It's more involved and not as simple. I'll manage. Thanks for your help.