I had some ideas for systems to "bring up" rookie soldiers, such that they would be useful as the game progresses and you can realisitically replace losses without throwing green meat into endgame combat...
Idea #1 Organizational Experience
Your men bring back their experience from the front line, they talk to others who have not yet been in combat, they provide training for the newer recruits. You could have a system where any experience that is earned in battle, is calculated and then a fraction of that (say 10%) is brought back and applied to new recruits. When fresh soldiers are recruited, this experience is damaged or reset, so you'd basically hire recruits in batches or waves. This makes sense, the next set of men are awaiting combat "around the corner" and are just waiting their final hiring into the main combat team. Once hired, the next set will need to learn and train. This gives you a reserve of decent soldiers (based on how much actual combat you've seen) awaiting recruitment.
Idea #2 The Jagged Alliance Method
As the game goes on, better soldiers are available for hire from more prestigous training schools for more money. Maybe your hiring "Militia" at first cheaply, but later gain the option to hire professional and even special forces soldiers. These will naturally cost more money, but come with better training and stats from the offset. This is much like how Jagged Alliance did it, as you could hire better soldiers for increased pay as the game progressed. The best soldiers would simply refuse to work for you until you've proven your worth.
Idea #3 The Mentor System
A buddy system where a recruit is paired with a more experienced soldier (must be 2 ranks lower) and gains experience at 75% of that of the soldier they are paired to. Effectively, your A-Team is bringing home their valuable experience for the B-Team to learn from, on a 1 to 1 basis. Fiddly to set up, but would be very strategic. Naturally, rank ups would occur only in combat, but stats could be gained which is the key thing.
I know that at the moment there is a weapon training system, but I am not sure this would matter in the case of an A-Team wipe, since your stats will still be awful. So here are some ideas I had for methods to provide that experience without the super-training of XCOM:APOC.