Not sure I follow… Are you saying that you have a Librem 5 with an AT&T SIM inserted, and that you have no 4G data connection ever? If that’s the case, then either AT&T’s coverage is bad where you are, or something is not correct with the phone’s settings (APN, etc.).
AweSIM currently uses AT&T’s network for coverage, according to Purism’s AweSIM page, so in essence, AweSIM is the same as AT&T in that respect. The network is the same.
AT&T might de-prioritize an MVNO (reseller) in times of network congestion, but that should only be temporary.
BTW, I’m also using an AT&T reseller (not AweSIM), in the L5, and I do have 4G data.
The wiki you linked indicates that people do get data with AT&T-based providers. (Although it needs updating now that AT&T has shut down 3G.)