Thought experiment: if Haskell were actually the One True Way, what would you expect to be different? Would you be able to tell?
To say "every language design has its own set of tradeoffs" implies that all languages are equal, but that's clearly not true; we can all think of languages that are worse than others. I'm not at all convinced that there isn't an overall best language out there (I don't think it's Haskell, FWIW).
'To say "every language design has its own set of tradeoffs" implies that all languages are equal'
I don't think that implication is there at all. It absolutely doesn't hold for strong notions of equality - strong equality of all languages should imply that they all share a single set of tradeoffs.
It also clearly doesn't hold for "equal suitability to any purpose", since something less suitable to the purpose may be traded off for something more suitable.
I think any general notion of "equality of quality" can probably be viewed as a special case of the above reasoning - we are picking a set of attributes, of benefits and drawbacks - but we've no guarantee that they all net out the same however we are measuring them.
Is there a best human culture? Clearly some are further down the tech tree than others, but...is imperialism really inevitable?
PHP isn't a bad language if its tradeoffs work for you. But you would be hard pressed to see anything good today in BASIC from the 80s (like we might miss things if we all of a sudden were sent 1000 years back in time). There is no best PL, but there are new PL technologies that make programmer experiences better; using a language that doesn't include at least a few of those technologies is probably going to be a handicap (compared to your peers who are using them). Haskell is bit up the tech tree, but not incredibly so compared to other modern languages like Scala and even C#.
It's politically unacceptable to say so, but some human cultures are clearly worse than others, and yes, I expect there probably is a best culture. I wouldn't begin to guess at which one that is, but I would take people seriously if they're saying that a particular culture has got particular things right and other cultures can learn from that. The problem with imperialism was less the culture and more the exploitation and theft, which is not really relevant to the programming language case.
There is probably not a best culture (though there are definitely bad ones), just cultures that are further down the tech tree and therefore can out compete other ones. The same is true with programming languages.
To say "every language design has its own set of tradeoffs" implies that all languages are equal, but that's clearly not true; we can all think of languages that are worse than others. I'm not at all convinced that there isn't an overall best language out there (I don't think it's Haskell, FWIW).