This question is often asked with respect to Sanctuary, Protection from Evil, and other effects that refer to an "attack."
Luckily the core rules answer this in the Special Spell Effects section of the Magic rules.
Attacks
Some spell descriptions refer to attacking. All offensive combat actions, even those that don't damage opponents, are considered attacks. Attempts to channel energy count as attacks if it would harm any creatures in the area. All spells that opponents resist with saving throws, that deal damage, or that otherwise harm or hamper subjects are attacks. Spells that summon monsters or other allies are not attacks because the spells themselves don't harm anyone.
So since anything that provokes a saving throw counts, Murderous Intent counts as an attack spell.
The Complete Warrior spellsword is an exceptionally weak class. Entry requires at least one lost spellcasting level, and getting to 4th level requires two more. Lost spellcasting levels are like death to a spellcaster; in most cases it is optimal to never ever not even then lose spellcasting. So to begin, let us keep that in mind.
Furthermore, after the publication of Complete Warrior, similar concepts were produced in Wizard’s Player’s Handbook II with its duskblade, and in Paizo’s Ultimate Magic with its magus. Both of these are base classes, and their versions of Channel Spell (called Arcane Channeling and Spell Combat, respectively) can be used at-will, rather than Channel Spell’s tight per-day limit, and can even be used with a full-attack.
In comparison, the spellsword’s Channel Spell can only be used 3/day at Spellsword 4th, and it requires a move action, which means it will almost certainly preclude a full-attack.
To get 3 rays from scorching ray, the spellsword needs CL 11th. Getting into spellsword and progressing it to 4th causes three lost spellcasting levels, so he’s a minimum of 14th level at that point.
A barbarian at that level would have Strength around 30 while in Rage (18 to start, +6 from Greater Rage, +6 from a belt of giant strength), and could trivially use Power Attack quite safely for substantial damage. Using a two-handed weapon, he’s looking at around 2d6+40 damage for each attack.1 That matches your 47 damage exactly, but it could happen up to three times in one turn. Unless the spellsword lost even more spellcasting levels to get more, he can only use Channel Spell three times per day.
A spellcaster, meanwhile, could cast scorching ray for 12d6 damage... but it would require only a touch attack, and could happen at range. Touch attacks are dead-easy to make, so a spellcaster should hit with all three. This loses out on the weapon damage, but targeting touch AC is so much easier that the expected damage goes up, not down. But more importantly, a 14th-level spellcaster has much better spells to use. Disintegrate would deal 28d6 damage; that’s an average of 98 damage.
And that’s just pure damage; spellcasters are far more formidable when they don’t deal damage. For example, he could easily haste the barbarian to give him another shot at that 47 damage attack, and it’d hit the druid, the druid’s pet bear, and the rogue, too – easily adding over a hundred damage per round just from the extra attacks all these people get to make.
So yes, you’ve understood the rules of Channel Spell correctly, and no, it’s not powerful at all. Spellsword is considered to be an at-most one-level class (for +1 BAB, +1 level of spellcasting, and 10% ASF reduction), but taking more levels is a mistake, one that even Wizards and Paizo recognized and fixed by publishing duskblade and magus, respectively. To “downpower” the character even more is a bad idea. The class itself already does that too well.
- Damage derivation: 2d6 (greatsword, average 7) + 1½×15 (Strength, two-handed) + 1 (enhancement) + 5 (collision property, mostly for easy number) + 12 (Power Attaack, taking −6 or −4 penalty in 3.5 or Pathfinder respectively) = 47. Note this uses only two items (+1 collision greatsword and belt of giant strength +6, 54,350 gp out of 150,000 recommended for that level) and one feat (out of five); the number could be much higher with a complete build.
Best Answer
Yes, they are affected by spell resistance
Even though those spell-like abilities, elemental ray and acidic ray, have no spell to base themselves on, spells (in general) and spell-like abilities are subject to spell resistance, unless otherwise noted.
Spells from the conjuration school can mostly ignore spell resistance, and spell-like abilities based on those spells follow the same rules. So a spell-like ability that duplicates Create Pit, which ignores spell resistance, would also ignore spell resistance. This can be seen on the topic When Spell Resistance Applies:
But spell-like abilities that do not duplicate a spell (like elemental ray and acidic ray) follow a more general rule, with their spell level based on the highest spell the character can cast, as per this FAQ on SLA's: