Tell me the maps on which you think is better to enable lifes because defenders win all times.
I cant tell u this, because looking on concrete maps is wrong way, on my opinion.
I will try explain my thoughts.
As i said above: best joy experience we have when both teams have closely equal chance to win.( Otherwise one team will
be bored, and another will be angry,sad or bored too.) So, our goal is to make every played map more balanced. What things can affect on this? - Castle, fractions, ratio of good players in each team, lives, round time, time to spawn(actually, i dont know about ability scripts to change this last two, just guess ). Ratio of good players and fractions on map are totally random, we cant handle with them, but they do major effect on balance on every map. Effect from current castle(map) are very less and very depend from that two, so talking about balancing some map has no very big purpose.
Well, we have only last three impacts, that can be using in scripts(i guess) for real-time auto-adjusting control. Idea to change round-time limit is not nice. And idea to change spawning time is very attractive, but need good thinking about it(for example, maybe we can combine it with lives and make lives-limits with 30 sec spawn, and when they go out, every next spawn able after 90 sec). At last, now we have only one available way to make automated control of balance, and it is in lives-limits. And i think, its should be used in every map(and start already with limitation, and then go limitless or lower).
Lifes isn't only a limitation for who is playing, it's also a limitation for who joins the game after minute 6th when they get 0 lifes and they've to wait several minutes to play.
Maybe better use some formula like this for joined players: lives_limit_for_joined = (current_time_left/round_time) * current_lives_limit
(with rounding to integer, of course )