Its more the way bowlers take wickets that is important. For example if Milne is taking wickets by beating batsmen for pace he might run through most domestic teams and teams such as Zimbabwe and Bangladesh. However if he played England/Australia/South Africa he would find the opposition would have no problem for his pace and he would struggle to take any wickets. Arnel is a good proof of this theory.
Conversely if Milne was taking his wickets by a combination of swing/pace/seam and hitting good line and lengths, then he would bowl fine against those said nations.
Same with batsmen, some might smash our domestic bowlers all over the park, but when they come up against international bowlers, they get ripped-apart because their technique isn't up to it.
Imo you judge a player on a combination of technique and performance, before Milne makes the squad he needs to settle into a consistent line and length alongside at least a nibble of swing or seam