It's not a myth. What part of it only teaches you FOCUS FIRE. did you not get? if it taught you anything that equated to T10 you'd see everyone running full 15v15 Deathstar strats or 15v15 all medium TVP/Batchat strats..........
Actually the last I have seen from a few Top Tier clans. and the auto loader focus fire can finish a team pretty quick.
Point is T6 CW doesn't do anything to teach you about end game CW play outside of focus fire.
I think you're a bit dogmatic in how you present it, but your point is interesting. Perhaps, the better way to express the issue is that the concepts that are most prevalent in tier 6 are not the concepts that are most prevalent in tier 10? For example, passive scouting is a viable option in tier 6 that offers a usable form of map control. However, passive scouting is much less effective at higher tiers due to the often-cited view range creep at higher tiers. Obviously, we have little insight into what would be a perfect game in WGs eyes. Perhaps we should ask "Is passive scouting meant to be part of the game? Or is it a form of play that exists due to the circumstances of the tier 6 meta?"
I would like to also question the seemingly prevalent mindset that all roads lead to tier 10. I understand that they are the top of the tree, but does that make that level somehow inherently suggestive of more skill? I might argue that they are simply a different meta, and that what makes tier 10 generally more complicated is the larger usable tank pool, which allows for admittedly greater variation in tactics. Perhaps that is by design, but why put up the economy barrier if the higher tiers are meant to be the more relevant tactical arena? Logically, players exist whose participation in the "endgame" would generate value regardless of how much time they have to grind. On the other hand, surely people would not pay for premium accounts if they could afford to maintain their in-game currency needs and be able to perform at the purportedly more venerable "endgame" level.
Perhaps a good solution to getting more of the player base interested in the "endgame" arena would be to make the economy of the competitive high-tier arenas more forgiving. Although, that might lead to poorly-skilled players infecting the "endgame" arena in which all TOP CLANS congregate.