Flawed logic.Again, that's not a true statement. The spear has had at least as many variants, to the extent that variants on a design are a countable thing anyway.
Just because this was true in the past doesn't mean it will be true in the future.
Really you could have had the same conversation 1000 years ago.
Person A: "Spears have been around for a long time, are the dominant weapon all over the world, and have tons of variants. Swords and bows are around, but spears really dominate. Do you think there will ever be something that replaces the spear?"
Person B: "Sure, eventually someone might invent something completely better that will replace it, who knows what the future will be like?"
Person A: "You don't understand, every time someone had a new invention (i.e., the axe) it always ends up better when combined with the spear (i.e., the pole-axe or a halberd)"
Person A was right about his own time, and the past, but not about the future. The fact that person B didn't describe guns doesn't make person A right.
Spears were in many cases weren't alone for long and were replaces or became a compliment themselves.
Guns have not, and even weapons that don't fire bullets are often still "guns" in design.
This is precisely why that many new weapons or "launchers" still have a base form of a gun because of ease of trigger design.Something that would seem difficult to improve upon is the pistol grip and finger activated trigger that are both extremely ergonomic.