Generally I treat XIV variants as intended for pitched battles where it'll be a long slugfest with little room for movement. That's where the little things like armour, flux and especially OP put them on top of their stock variants.
Only XIV Falcon is worse than base version, because it's only advantage over Eagle is speed. Significantly reducing this advantage makes Falcon XIV meaningless.
It's not really competing with the Eagle too much as-is given it has a lower deployment cost. It's more of a role change to suit what I said above, than being worse.
Any ship will become better with officer sand correct loadout. I just finished a playthrough using only xiv ships. I realized that no matter what officers you bring, or loadout you equip, they will bring 0 difference from their original counterpart (except the legion and maaaaybe the onslaught) but anything lower than a cruiser is a net loss.
I wouldn't call xiv ships as "collector pieces" because in a space battle game, a collector piece is expected to be a rare and unique ship (mechanically and performance-wise) the xiv, other than the legion, are just orange with a bad hullmod.
A small difference is the intent. It's a variant that gives generally a wide statistical advantage at a small price, all while doing no harm to the deployment and maintenance costs, under no circumstance is this a 'net loss' unless you're perhaps building for something ultra-aggressive and mobile like SO. If I could apply this 'bad hullmod' to every ship I would in a heartbeat just for the OP boost.
As for collector's pieces, the value is in them being somewhat (at least initially) more limited than the normal sort, as well as their historical significance in the game's world.
Spoiler
The XIV Legion is also no longer an exception, given the Historian can point to it's blueprint now.
