I personally feel that this idea of the successful DW team being ttar / exca / chomp / chandy / breloom / keldeo or genesect or whatever is extremely misguided. The vast majority of teams are not like that, and the vast majority of the teams that ARE are made by people looking for the "easiest team style". DW has been touted as being one of the most diverse metagames, and i think that still stands. As j7r said, the 1337 stats are hugely influenced by the existence of alts among high-ranked players--hopefully this can avoid sounding self-congratulatory, but I for example had four accounts in the 1337 range and used fairly close to the same team laddering all of them, which I did quite a lot (that team being composed of 6 of the 7 top used pokes). Add to this the fact that DW has a much smaller playerbase than OU, the tier it's being compared to, and things like multiple alts can hugely distort the usage stats, particularly in 1337, where the number of people using alts is higher and the total number of players is lower.
The chandelure thing is a notable issue, but I personally think that an opinion of its brokenness in shaping the metagame is (no offense intended) a sign that one has not engaged in a lot of high-level play. First of all, tyranitar does not have 70+% usage in the 1337 stats because of chandelure. Sand is an extremely potent strategy even in OU, and DW's banlist just accentuates this, as does chandelure's presence--but it is not responsible solely or even majorly IMO. Secondly, given that sand is such a powerful (and, to be fair, easier to use in general) playstyle, for less experienced players looking for an answer to chandelure sand is an extremely natural choice--this does NOT qualify as over-centralization. Third, chandelure's impact on the metagame in other domains is not nearly what others seem to think it is. Tyranitar's mere presence on ~80% of 1337 teams (again, independent of chandelure) means chandelure will be restricted to 1 kill a match, and even then it struggles. Does *having to* run shed shell on your skarmory really count as over-centralization? I don't think so. Many players run shed shell on skarmory even in OU because of magnezone. If it were more popular, I'm sure so would be shed shell. As it is, *dictating* what is a popular item on a particular type of wall seems far from over-centralization to me--by this definition, I would expect something like rocky helmet on ferrothorn to be called over-centralization of rapid spinning and volturn. In high-rated battles, chandelure is usually only present on a team for the purpose of covering a team's weakness to specific pokemon such as gliscor or breloom, neither of which usually hold shed shell for obvious reasons, gliscor's being toxic orb or flight gem and breloom some power-increasing item.
Superbadd, while it is true that defensive teams are less popular in DW than offensive ones, how sure are you that this is attributable to chandy? Offensive teams are just plain easier to use, and as I explained above, sand offense is the most obvious playing style, especially to newer players. Furthermore, just before BW2 there was an outbreak of stallesque teams featuring heatran amoonguss slowbro cores. A good example of this is
metagross66's team, which peaked #1 before the server shift (notice that only 1 poke in a full-on stall team has shed shell). The fact that stall is less common in general is in my opinion a comment about the metagame and honestly limits chandy's usefulness.
I think sewa has the right idea here--the problem is that newcomers upon seeing the metagame just it by OU standards, in which exca, garchomp, and all the other might very well be broken. Together though, they just make it a tier with less stringent banning, a little closer to ubers than OU is. Of course, people never say ubers is a bad tier, because they are used to the idea of it being a different metagame and have accepted that the presence of all these pokemon that would be broken in OU allows for a metagame in which they are in fact perfectly suited. I actually like the DW metagame (before BW2, since when it has been somewhat non-existent) much better than OU's, and i think others would too if they gave it a try and stopped being...perhaps not scared, but how about trepidatious...of a different banlist.
And lucaroark, skarmory is a totally fine excadrill counter--in fact, (one of) the best. Of course excadrill will beat it in a last mon situation, but when having skarmory means that excadrill will never set-up and sweep your team unless it is the last mon, i think it can be considered an adequate counter and team support be relied on for the aforementioned situation. I mean, anything that can take 1 hit from +2 excadrill and do 70% damage works (since skarmory can BB exca to death after that, or anything with a good priority move. And in addition to skarmory, there do exist very solid excadrill counters. Even if +2 LO iron head can 2HKO gliscor, it easily OHKOs excadrill, and has protect to fish for more HP in case of a flinch. Bronzong resists every move excadrill commonly carries, and can 2HKO with eq. The fact that there is a short list of counters does not mean it broken--for example, terrakion in OU has much fewer counters (basically none actually if one does not know the set), but it is certainly not broken.
Sorry if this was a little long, just wanted to add my opinion on this topic.