Xue Sheng
All weight is underside
Good point, and there's more to it: some styles just can't be forced into the rule set without turning the style into something else. Sure, one could pursue the competition venue but you would not really be using your style the way it is designed and intended to be used.
This isn't a "deadliness" issue. It's just fitting into the competition venue.
I'll throw out something else here: How much does sparring resemble the real techniques of your art? It seems like many striking-based arts have a body of self-defense techniques and kata where the meat and bones of their fighting SHOULD come from. But whenever they strap on the pads and do some free sparring, everyone looks very much the same: modified (and often sloppy) kickboxing. Some people are more intense or less intense with it, but it all tends to look very much the same, regardless of the root style in which they train. From what I've seen, in the context of free sparring and competition sparring, very few people are able to use their meat and potatoes techniques from their self-defense arsenal.
So maybe competition alters EVERY art enough to where it becomes something else. Looks to me like competition has its own distinct style, and either you include that as part of your training, or you don't, no matter what your root art is.
Yet another example from xue using sanda/sanshou
There are different rules for different sanshou competitions and one could have trouble fighting in on mainland China that is rather successful in the US and vice versa. So rules can play a part in differences in certain sports matches. Take someone out of the College level Sanshou stuff in Hong Kong and throw them into a Beijing Sanshou match and it is likely they will get beat bad.
But sloppy sparing has more to do with someone not investing in loss to learn how to use it properly.
And in some cases competitions will alter an art if the competition side is emphasized over the traditional side. And if anyone wants proof of that look to TKD.