I completely understand your point, especially when you compare the materials and overall feel of an older Pro model with newer generations. However, I would suggest that we refrain from drawing conclusions based on rumours, assumptions, or comparisons based merely on appearance or limited personal observation.
Even the quality, strength, durability, and suitability of a material cannot really be judged simply by looking at it or handling a device. Such conclusions require proper engineering evaluation, including material testing, durability tests, structural testing, and long-term reliability assessments. Apple’s choice of material may therefore involve considerations that are not immediately apparent to the user.
The iPhone has earned its reputation not merely because of the material used in its chassis, but because of its engineering, design, ecosystem, reliability, camera capabilities, software support, and the overall experience it provides.
The iPhone is still a legend and a source of pride for its owners, and I believe it will remain so for many years to come—irrespective of changes in its design, materials, or price.
Ultimately, whether an upgrade is worth the price is a very personal decision. If an iPhone 13 Pro Max continues to meet your needs, there is certainly no reason to upgrade simply because a newer model has arrived. A great product does not suddenly become less valuable just because something newer is available.
Mobile brand/model selection is an individual choice based on many parameters—such as money, features, status, colour, aesthetics, utility, user-friendliness, availability, warranty coverage, service support, resale value, technology, and many other factors. Choose yours judiciously!