Your thesis is absolutely not true. Indeed, the iPhone 4 had a so-called "dead grip" problem, when the palm holding the device blocked the antenna and the smartphone lost the network signal. By the way, the problem was not only with the iPhone - almost every vendor, starting to produce smartphones in metal, faced something similar.
Since then, manufacturers have learned to avoid such troubles and the abstract modern iPhone is no worse and no better than the abstract modern Android smartphone when it comes to networking.
Of course, we can talk about the support of certain frequency bands and standards of communication and data transmission, about dual-band Wi-Fi or work only at 2.4 GHz - here all smartphones are different. But this is not a reason to say that certain devices are better or worse.
I have not met smartphones with pronounced problems in the operation of wireless modules for a long time, and dozens of various devices pass through me every month.
It is software established that the phone can only "see" networks with a good signal quality, because a poor-quality and weak signal consumes more battery power, which affects the phone's autonomy.