[1] https://www.abajournal.com/news/article/chief_justice_robert...
Under common law, there is no legal contract without a meeting of minds. There can be no meeting of minds without comprehension. Per studies of reading abilities, only 2% of Americans read at a college level. (See https://www.wyliecomm.com/2019/03/us-literacy-rate/ for a source.) Therefore such contracts should not be legally enforceable on the other 98% of Americans.
This reasoning applies only to contracts where members of the general public were expected to review the contract unassisted. By contrast in a business contract where both sides retained legal counsel, the complexity of the language is not prima facie evidence that the contract was unlikely to be understood.
If we decide that uninformed consent is still consent, we open a significant problem. And if we try to patch it by selectively applying the standard, we introduce arbitrariness which is an even larger problem.
Contrary to what you think it is very possible to have short legal agreements. The GDPR data policy basic template is quite comprehensive and rather short for instance, although it could get better. We could also imagine some informative shortened version with icons and standardized information in the same way you have for food components or drug warnings, or crucially apps permissions nowadays, that would cover 95% of the legalese in the user agreements.