WT seats in the A380 we flew in to Singapore with a 2 year old last week also don't have fully lifting armrests. We used a plane pal which was great, though it was an unusually smooth flight and we didn't get any turbulence seat belt notifications. The seatbelt was fine for takeoff and landing, We used a car seat the previous year and it was a complete PITA all the way through.

I'd fly WT over WT+ in this situation personally anyway. The additional "comfort" is moot and there are practical advantages in being able to confine a small child in a relatively enclosed space.