I just tried S1 E06: The subs work with MPC-HC, but stop working for my VLC near the beginning where the cat is cooking.

I don't expect it will be fixed.

Groups often only check their work against one video player.

It really depends on the nature and quality of the source as well as the way you're processing the raw before compressing it, and the compression settings. If you're working with something that has no grain and substitutes animation with slow pans of static imagery (*cough* Food Wars *cough*), it is very possible to reach visual transparency with low bitrate if you don't fuck it up. If you're working with a noisy/grainy source like Attack on Titan or some of the pre-digital stuff, technically you still can make it look good (that is, clean) if you go ham with filtering, but the noise will have to go. For many people is an instant no, but if low file size is your goal and proper denoising drops it by like 3/4, it's honestly not a bad trade-off in most cases.

Hi10 has some decent encodes and in rare cases they do make the default subs a notch better when no other group takes the show in question; it's just that a lot of their staff are used to taking the laziest ways out (such as transcoding an already significantly compressed source)—and even when they don't they rarely draw the line anywhere sensible with regards to size/quality ratio. E.g. what's the point of making an overcompressed 1080p "miniMKV" of an upscaled source justifying it with something like "well, it turned out small, anyway"?

As for ordered chapters in particular, I wouldn't care in most cases (I skip OP/ED about 98% of the time, so they're just dead weight to me) unless I want to use them with different subtitles—which is where problems tend to arise.

I don't consider OC a live tech these days.  

But the standard convention to tell if OC was used was if the torrent had OP and ED files, instead of, or in addition to, NCOP and NCED.  As was the case here.