I've said this before and I will say it again: Take everything you see on lolita secrets comms with a grain of salt. It is NOT a representative for the entire lolita community and some of them are even troll secrets anyway.
No one really has a real issue or 'hatred' with off brand. If there was any issue with lolitas wearing off brand it would be because a lot of the girls who wear off brand exclusively might not have the best coordination skills (not saying I haven't seen girls make brand look like a hot mess because I absolutely have unfortunately. Makes me sad :v). I honestly don't care what you wear or how big/small you are as long as you look good and it shows your making an effort.
As for bigger girls in lolita... Real talk: people will be talking/thinking about your weight. Lets not lie, this is the real world. But give them something positive to talk about and make your weight an afterthought. Wear a style that fits your body type, get clothes custom made/tailored for you - whatever you have to do. Yes it'll be more expensive and harder but it comes with the territory. A lot of them don't understand this really which is what bothers me. Heck not even some of the smaller girls get that last concept but whateves. xD;;
As for me I prefer to buy brand when I can budget it into my expenses. Its worth the money in my opinion because I know what I'm getting. I know that I don't have to fuss with it to get the right shape or alter it as far as style. It makes it feel more legit I guess, too. I know girls who exclusively wear brand but they don't knock others for buying off brand. I say if it works for you and you look fabulous go for it! The majority of lolitas have a mix-match of offbrand and brand anyway so its no big deal. Things get exaggerated on the internets.