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).
这实际是no more……than，no less……than的句型。
no more…… than的意思是"与……一样不……"或者说是"两者都不"，no less……than有两个意思:1，不逊于；2，不外是。
而worse本身具有否定意味，所以基本等同于no less …… than ，这句话的意思就是:5g的速度并不逊于4g……
由于 A is no better than B = A is worse than B是出于夸张语气，其实真正想表达的意思就是A is no better than B= A is as bad as B，中文可直译为「A没比B好到哪里去」，也就是你老师那派的观点：「一样差」。但是明显这里问题里不是「no better than」 而是「no worse than」！由此可见，你老师那派的说法是错误的。
在第二段里，这位截图里的答主和他楼上的答主都认为，在实际生活中，不会在Q很糟糕的前提下使用「P is no worse than Q」这种说法，而会直接使用as bad as的说法。所以这里也能说明你老师派的说法有误。所以这个短语的意思总结一下就是：1. P没有Q那么差， 2. P和Q差不多一样好（前提是Q也不错）。
