No, they're really not, not if a classless system is already full-featured. I can put together a new archetype package in Hero in 20 minutes and be pretty sure it'll work, because I'm using nothing but components already available for use in the system. Same to a lesser degree in GURPS.
Its only a problem in systems where you have to invent new components out of whole cloth in the first place. If a system already has the tools to make a Beastmaster, then the Beastmaster Archetype is just pre-constructing it for them and making sure all those components are already in place.
The problem is that in a point-based game like GURPS, options need to be individually balanced with one another and costed accordingly. In a more restricted class-based game, you can balance whole packages against one another.
Take Pathfinder 2e. Each class is fairly strictly siloed off from every other class. There's a lot of wiggle room within each class, but the walls between classes is fairly strong. You can use multiclassing rules to trade in optional class features for some features of another class, but those are limited for the sake of balance. That's because mixing class features between classes would lead to overpowered synergies.
For example, most martial classes have some mechanic for inflicting additional damage. Barbarians have Rage, Rogues have Sneak Attack, and Fighters have an overall better attack bonus (at least with their weapons of choice). Both barbarians and rogues deal more damage
per hit than fighters, but fighters hit more often, so they overall deal about the same amount of damage. But if a barbarian or rogue could access the fighter's improved weapon proficiency, they'd both hit more often
and deal more damage per hit – so that bit is out of bounds for multi-classing. Less martially inclined classes can multi-class as fighters in order to get a broader weapon proficiency, but not
better. And while multi-classing into barbarian or rogue gives you
some rage/sneak attack benefits, those are much lesser than those a full member of the class can get. In a more free-form system, you'd need to account for characters who both have high accuracy and high damage, and likely the optimal path would be to get a bit of both.
And that's just in the narrow context of hittin'n'hurtin'. If you move into more esoteric things, GURPS at least tends to vastly overvalue abilities that rarely see any use. For example, Catfall is a 10-point advantage in GURPS, reducing falling distance by 5 yards before calculating damage and allowing a roll to halve the remainder. Same thing with breathing water, another 10-point advantage (though it's not obvious in the system: it's the "Doesn't breathe" 20-point advantage with the -50% modifier for only working in oxygenated water). Both of those are basically "ribbons" in D&D – things thrown in for free for some color, but not expected to move the needle balance-wise.
