So, to start off, I'll briefly tackle the status of the Helots. The belief that Helots = ancient serfs was a long-held belief in academia, one that has largely been abandoned in modern studies of ancient Sparta. I go into the details here and here. To these, I would also recommend this new article by David Lewis, who argues for the origins of Helotage within wider Greek practices depicted in Homer (ca. late-eighth to early-seventh century BC), i.e., that Helotage was simply another type of slavery that developed along a different trajectory from the better attested 'Athenian' chattel slavery. Unfortunately, he has not yet uploaded the whole article to academia, but he may provide you a copy if you email and ask nicely.

As for the Spartans' treatment of Helots, I go into that here. Ultimately, the attestations of this supposed harsh treatment of Helots come from later authors and may represent later developments or literary inventions. Classical Athenian writers who do state that the Helots were treated harshly do not actually state how, so there is no way we can verify their claims. However, from what we know of the Athenians' treatment of slaves, such as brandings, torture, and rapes, Athenians' slaves did not exactly have it easy (I go into detail on some overlooked evidence on the Krypteia here).

[From an older answer] I'd even argue that, at least in the late Archaic and early Classical period, many Helots, particularly those living in Messenia, were actually better off than slaves in other parts of the Greek world (as better off as a slave can be...). Spartan absenteeism, which saw Spartans spend most of their time within Sparta itself, meant that Helots were possibly left to manage their own affairs, possibly under the management of a Helot overseer, or a perioikos. A similar situation likely existed throughout the Greek world, but masters elsewhere would have been able to visit and manage their slaves much more frequently, increasing the likelihood of abuses and punishments.

Of course, it is important to note that the situation was likely not universal for all Helots, with those closer to Sparta receiving more attention from their masters than those living further afield, across the Taygetos mountains, for example. I go into the issues of Spartan absenteeism and Helot autonomy elsewhere.

As for Pollux and Athenaeus, I would not put much stock into what they say about Sparta or Helots. As you say, they are remarkably removed from Sparta's prime in the Classical period, and Spartan society underwent significant changes in its later period, despite claims of it remaining a static system. David Lewis, who I mentioned above, also provided a brief but comprehensive discussion of Helots for the Oxford Classical Dictionary.

I hope this answer, and my other linked answers, help provide some clarity regarding the Helots. If you have any further questions, do ask and I will endeavour to answer.