Shield Bash I’m having trouble picturing as gaining a niche. The slight damage increase is simple not worth a perk point. The damage would only matter if the enemy is close to dying, in which case you might as well just hit them. Stun is still the most fitting thematically, but as noted before that might make it too powerful and infringe on other means of stunning. It would probably make it a must-have for shield users.
– Give it stun. Make it a defence tier 2 perk that replaces of Nine Lives. Make Nine Lives an utility tier 1 perk. Important to note that I’ve personally never had Nine Lives make a difference when it actually triggered, so I’m not sure if it’s too powerful for tier 1.
– Give it an accuracy bonus so that you can use shield bash more reliably. Have it do a bit more damage.
– Replace it with another perk
Shield bashing has a built in accuracy bonus of +25 over standard attacks. If you take the perk, shield bash becomes a high accuracy attack good for finishing off enemies already gravely wounded .
I’d suggest rather than stunning the target, the target gets a -10 reduction to their melee offense and defense for a turn to represent being off balance.