Tarantula's relatively low burst damage is its greatest weakness as AA I think, and it is a pretty bad weakness for missile AA to have. One needs quite a lot of (expensive) Tarantulas to shoot down a Thunderbird before it fires, or a Licho before it is well on its way home.
Tarantulas are also expensive enough to be a pretty juicy target for Lichos, which can be a big problem if you don't have quite
Tarantula received some buffs (mostly to the speed and agility of its projectile) in 2019 and 2020 and has perhaps never escaped the reputation it earned for unreliability before those changes. Looking at its stats now it is a stronger unit than I would have guessed. Still, I'm inclined to agree with the opinion above that among the ground mobile missile AA units, Angler is top tier. I'd probably also prefer to have Crasher over Tarantula unless terrain is a big issue.
(Flail is much weaker since its AoE nerf. Vandal in theory has good stats for cost, but the sheer number of them you need to pose a threat to bombers makes them cumbersome and relatively easy to avoid.)