When we say that "A is no worse than B", then again by strict logic this means that A is better than B. In practice we would not say this when B is very bad .
Wed tend to mean that A is not quite as bad as B. It can also be used when A is good and we want to say that A is almost as good as B.
eg：
My son is usually no worse at chemistry than your daughter (who always gets at least a B+), but on yesterdays test he did exceptionally badly (he only got a D).
這實際是no more……than，no less……than的句型。
no more…… than的意思是"與……一樣不……"或者說是"兩者都不"，no less……than有兩個意思:1，不遜於；2，不外是。
而worse本身具有否定意味，所以基本等同於no less …… than ，這句話的意思就是:5g的速度並不遜於4g……
由於 A is no better than B = A is worse than B是出於誇張語氣，其實真正想表達的意思就是A is no better than B= A is as bad as B，中文可直譯為「A沒比B好到哪裡去」，也就是你老師那派的觀點：「一樣差」。但是明顯這裡問題里不是「no better than」 而是「no worse than」！由此可見，你老師那派的說法是錯誤的。
在第二段里，這位截圖裡的答主和他樓上的答主都認為，在實際生活中，不會在Q很糟糕的前提下使用「P is no worse than Q」這種說法，而會直接使用as bad as的說法。所以這裡也能說明你老師派的說法有誤。所以這個短語的意思總結一下就是：1. P沒有Q那麼差， 2. P和Q差不多一樣好（前提是Q也不錯）。
