Here’s a web graphic for password complexity levels. And another forum post that has relevant info. LUKS2 on any decently up to date system uses argonid by default nowadays so no need to worry there. This hashing algorithm requires memory in addition to compute which slows down unlocking time when putting your password in which also slows down attackers who can buy arrays of GPUs to do a bunch of compute but are more constricted on memory.
For a deep dive on this subject read Security Now! Transcript of Episode #388 . Search “Leo: Very nice. Memory hard problems. Not hard memory, memory hard.” to jump to the discussion point. Now you also have to rely upon the program’s correct implementation which may be a reason to use two encryption technologies for the extra careful person. Though this adds to the complexity of the whole process: access (more complicated setups lead to greater possibility of user error), maintenance of the codebases and therefore the number of tools you need to keep up to date on. It doubles the chance for code to go wrong in terms of data integrity; however, scrambling data twice isn’t inherently hazardous. As long as you use trusted, well-audited tools they should do the job reliably however many times you stack them. I’m just trying to get across that simplicity as a security feature shouldn’t be overlooked.