But when the two are mutally exclusive on a fundemental level, you just can't. By the nature of Chaos being fundementally "oh no, you can't win" and Lagann, is, to my limited knowledge, explicitly "oh yes, we can." There's no meaningful way to quantify that sort of conflict - it's all about preference.
You can be more objective when there are observable, quantifiable results to look at (or even better, numerical ones), but when espousing infinite verses infinite...
(For the record, I don't believe for even a heartbeat the Chaos gods are truly that invincible; the first and most glaring point is if they were, the Emperor wouldn't concern them at all: yet if what I've read is correct, if the Emperor were to regain his full power, he'd be able to beat the Chaos gods to death with their own internal organs (which he would make them have specifically for the purpose...) Or the C'Tan, which were supposedly on a similar level... The whole "chaos will always win and corrupt everyone" sorta falls apart in 40K, where you categorically have powers that are equal.)