So, the other interesting bit about this is, is for a Spellsword who has access to "Combined Strike" its effectively 72 build to get access to a "United Strike" (and some rogue skills & defensives as well) -- which is more than double damage, and scales off any weapons profs they have as well. And swings body, so its lets an earth Spellsword have a non-necromancy way to do a lot of damage. This may be idle speculation, given that this a 250+ XP build minimum; but you could have an spellsword archer throwing 10-12 from the front and that if they made use of unite strike, could be doing 100 body packets for as many 9th list spells as they have. And its likely with that build you'd have a good chunk of defensives from both stealth & martial. And if you were inclined to buy more base damage for the bow, weapon profs give 1.5 damage per. And since profs go up in cost, for an archer, there is probably even a time where buying your first backstab is cheaper than another weapon prof - at 4 weapon profs, your first backstab costs the same as your 4th prof.
The interesting change to this versus the old rules is that the defensive ability purchases are based off XP spent in stealth skills, not backstabs. So yeah, as a Spellsword you can only get 2-3 backstabs for 60xp or less, but you can get 2 backstabs, 2 evades and a dodge for 60xp, and this qualifies you for United Strike.
Honestly, I'm not sure how useful it is to speculate about the power of builds that don't really come in to their own until 300+ XP. It seems likely that at that power level, things get hard to compare.