Ryukishi is way too modest for his own good, by saying that at the end of his message. The only bad parts I’ve ever found in Umineko were very selected lines with sick jokes from Battler (either involving Maria or just being a pervert in general) and some random humorous moment during Goat-kun’s adventures in which it kinda makes him into an admitedly lolicon for a split second.
One may argue the “shounen battle” writing from Gamemaster Battler in EP6 and EP8 is kinda overdone too, for me it was fair enough considering the context.
In each case, the things are so minimal I don’t think it’s even fair for him to be harsh on himself to the point of calling them shabby. But welp, who is me to judge how the own author see his work (it just hypes me even more for WTC5, as he is apparently pointing out some “laziness” from his own, which makes me eagerly wonder how better he can even get after the latest WTC).