Agree and disagree!
Waiting for the hubs to cool down before entering the water is an excellent practice for the reasons you mentioned. Not many people know that or they are just in too much of a hurry to care.
Greasing as often as you do is not the same as a physical inspection every year preferably in the fall. This eliminates any water in the hub from freezing during winter storage. I know you are being careful not to over grease but most are not. You recognize these folks by the amount of grease splattered on the wheel, or worse... underneath the hull from the rear seal leaking...or worse than that...a seized brake hub from grease leaking past the rear seal onto the shoes creating all kinds of fun!
19 years on the same bearings👍 is probably due to the quality of the bearing made 20 years ago vs. those used today.