The idea that all players have this SP wall IMO really hinders strategy more than helps it. Because then you have strategies that abuse this.
Would it literally be so much to ask that a defending player drop ONE cheap critter, just to keep IA at 1 SP for his opponent, and pay 1 SP for two more turns to keep it that way?
Considering that by punching away at your opponent's LP, you already trigger some of his or her SSs (and if your opponent is building his or her deck around the fact that "I'm going to get rushed, get hit, and then win later with some I-win-unless-I-get-rushed-out combo-except-I-have-anti-rush-SSs"), that's a massive advantage.
The 1 SP iczer attack under all conditions simply removes player interaction.
"Tick tock if I get to X SP, I auto-win with some grim combo"
In the meantime, the rushing player has to deal with all kinds of probably hideous SSs (Scylla, assassin, who knows what else)
This seems a completely one-dimensional deal.
Nerf Elite Fencer. Change start skill to "target unit of agi 4 or higher gets AGI = 3. Then, this unit gets AGI = 4 for this turn and ATK +10"
For the great justice of the diverse meta.