The minion infusions are based on the 'class' stats, so the range infusion gets boosted by dex, melee infusion boosted by str, so could see where you might have your tank/archers also spend a point to get access to those minions.
The Incarnate stats don't scale off of the Summoner's stats. Only the Summoning Skill and the level of the caster matter. The caster's Intellect, Finesse, and Strength are not used at all. You can right-click an incarnate to inspect its stats to confirm this.
That being said, tanks and archers make just as good of summoners as anyone else. Exactly the same even.
A little puzzled that bullrush scales with dex but tentacle lash scales with strength. If anything, it seems like it should be the other way around.
I thought the same thing. It turns out, Bullrush is a weapon-based skill. It scales off of Finesse for most people because the template starts using a Spear, and they are Finesse based. Use a 2H Sword or Mace instead and then all (both) of their damaging abilities will scale off of Strength.
Tentacle Lash is not a weapon-based ability, and therefore doesn't take the character's weapon into account.