The fighter weapons are the highest single-target DPS weapons out there. So comparing anything else is a little silly.
But yeah, I too am a fan of the techniques, but found them underwhelming at first. After taking force and techter to level 12, I decided to carefully weigh my options, and made the decision to take Ranger up to 20. But after doing so, came back to techter.
Techter as a main class offers Shifta/Deband. This is a party-wide 5% damage boost, 5% down boost, extra natural PP regen, and 10% less damage taken to every ally in range that can be kept up constantly. As a side note, techter main offers 40% more healing and shares heals with allies in the area. Force offers Photon Flare. Which appears to offer 20% more damage (through potency) for 30 seconds on a 3 minute cooldown. There is also a lot of natural PP regen there available (at a reduced rate) as a subclass force, too. Ranger offers blight rounds, which creates a weak point at the target location on-demand that increases damage to the particular location by 20%.
To be honest, "natural" PP recovery feels like a bit of a trap. Most of the time one can only recover PP naturally by standing still or moving without photon dash. In other words, it only helps recover PP when idle. Sub gunner with its active PP bonuses makes a lot more sense, as I don't want to be idle on the battlefield when I can help it.
Shifta/Deband offers a lot of boosts, but each of them are very small. 5% extra damage, and a total of 10% extra down (1.05*1.05), plus small defensive options. The only trouble here is that while they can be maintained constantly and affect every ally in the area, the bonuses are still small. It can be hard to notice unless one is a min/maxer whose trained to keep an eye out for those buffs.
The ranger option is probably something you aren't expecting, as it's a ranged class and not a technique class. That means most likely using a sub force in order to use the rod and techniques. Also it means that the techniques itself will be about 9% less effective as you aren't getting the main-class bonus to them. On the flipside, Blight round allow you keep a 20% or 25% bonus damage on a specific part constantly while doing a good chunk of damage by itself. Everyone gets that bonus damage as long as they hit the specific part targeted. A rifle is required, so this option is specific to ranger/force using a rifle/rod multiweapon. The good news is that both the rifle and rod are 4 star Foursis series weapons, so it's not difficult to set up.
I however ended up ranger/gunner for a while using an unmodified rifle and launcher. Damage was great, especially from the launcher, but I ended up missing the elemental down option techniques have. That is the one thing that makes techniques worthy of boss battles. Do enough damage matching the elemental weakness and you can force an elemental down on the target. This acts like a down status, but is separate from the normal down from high damage. So the enemy boss can spend a lot more time downed than usual.
But that's my opinion.