They do have a sneaky jink generator! XD I believe they are called holo-fields and they add +1 to the cover save. So moving normally gives a 4+ and flat outing gives a 3+ cover save.
The wave serpent is an amazing vehicle. Do not be discouraged by these underwhelming reviews. Its durable, offensively powerful, a transport, and highly mobile. It may be a perfect unit!
Durability: It's AV12 so it takes S8 to S9 weapons to reliably penetrate its front or side armor. Anyone will be quick to point out that most armies have access to lascannons or missile launcher equivalents, but how many armies can spam them? Why spam them, you ask, when it only takes one lucky shot to blow up a vehicle? Well because of the Serpent Shield, one of the most incredibly useful pieces of vehicle wargear in the game. What it does is make all penetrating hits glancing on a 2+! So a balanced army might have 4-8 strength 8 or greater weapons. First you have to hit with those weapons. Lets assume 8 shots for this scenario and BS4. So 6 shots hit. 3 shots glance or penetrate, and then half of those are ignored through the increased jink save and then most likely the rest are reduced to glancing shots.
Let me recap. 8 S8 or 9 shots equals 1-2 glancing hits against a Wave Serpent. That's not even enough to glance it to death! These vehicles are insanely durable.
Offensive Power: They come with 7 S6 shots that will all essentially be twin-linked and 3 of them ignore armor saves on a roll of 6. Then if there's not anti tank weapons in the Serpents field of fire it can unleash a further D6+1 S7(6?) shots with pinning. Which can also be twin-linked. Wave Serpents can wreck havoc on light transports, any kind of infantry, and even flyers with all the twin-linking.
Transport: It's not a tranport that shoots. Its a tank that can transport!
Mobility: You get all the tactical flexibilty of a fast skimmer to deliver troops or fire power anywhere on the battle field.
Do not underestimate the Wave Serpent as it is currently, in my opinion for the above reasons, one of the strongest vehicles in the game.