The most important class in the game stopping at tier 2 is very unsatisfying, giving it a third tier not only adjusts its power level adequately but also gives old players something fun to grind.
Engineer III Class β 21 - 20 - 16 (+5, +4, +0)
This adds +3 green perks compared to engineer II strengthening them exactly where they need more points the most, as they automatically require 12 points into fast building leaving only little left.
Starter perk: + 15% building speed
Top tier classes come with perfect starter perks, so should engineers. Faster building speed makes them not only more fun to play but also incentivizes players to do more engineering, leading to more social & functional games.
(optional) Special feature - Motorized Engineers
To make the Engineer III squad more fun & creative, they can come with a truck, similar to APCs but without any weapons or spawning abilities. The squad structure & upgrade trees stay the same as engineer II.
β mechanically & historically reasonable, as engineers carrying tons of steel around makes more sense if it comes packed in their truck. also makes them more mobile and helps creating flanks with rallies/structures much more realistic. balance is kept by not giving them drivers/spawn ability as APCs have.
The squad coming with the truck is perfectly set at BR2. Motorized engineers also enable the addition of fun & creative event/premium squads (possibly as mechanized engineers with armored vehicles but without MGs/cannons. unique weaponry like smoke launchers/ampulemots could be used though).