It’s not even that. The whole new system is flawed and not very well thought out.
When they will hear about this reserve trick, they will probably call it a bug and e.g. exclude reserves from being used for calculations. So there are ways to fix this.
But this whole system is just stupid. Let’s say you want to play a 2.3 BR plane at 2.0 BR. You can create a “lineup” like this one:
Spoiler
This way I reduced my BR to 2.0, and I have no intention to play the 1.7 BR plane. It’s there just to reduce my BR.
Let’s say I die in the battle early, and since I only used my 2.3 BR plane, the 1.7 BR plane will get crew locked and my lineup will become a 2.3 BR, right?
Spoiler
You can say, it made the difference, it’s now working as intended. I can’t play at 2.0 BR anymore, because I have the 1.7 BR plane crew locked. A huge victory for the devs?
But don’t get too excited. I have 5 crew slots on my account. There is nothing that stops me from… adding another 1.7 BR plane to my “lineup”:
Spoiler
So I can start another battle at 2.0 BR again. And again, I have no intention to play the 1.7 BR vehicle. Before the next battle finishes, that first 1.7 BR plane will probably be already unlocked. And if not, I can add another 1.7 BR plane to this “lineup”.
This whole system is just stupid and not thought out at all.
The only difference is that more players won’t understand how this works and probably less players will use this system to their advantage, especially at the beginning (before they figure out how to do this).
The funny thing is that the devs have so simple and fair solution to just always use the highest BR plane as a lineup BR. Something that already works well in every other game mode.