Pyro3 -> Linker3 -> Sage would be better as solo boss killer.
The mechanism is that Fireballsx2>Duplicate>10s+>Fireballsx2>Duplicate = 8 fireballs at single spot, and then lure the Boss going in, as the Boss almost step in, you then link on the Boss with 8 fireballs and see His HP free fall instantly.
With 8 fireballs + 1 Boss or 2 Bosses (in mission), you need to link 10 targets, which LinkerC3 become necessary.
This is the best way to maximize the gameplay of Pyro-Linker combo.
But this build is good only mostly in Solo, or if you have companion in full support (perfect partner is Cryo3Chrono3 because they can help you buy time and snowroll your fireballs to boss for precise positioning). Because in party melee will just hit away your fireballs or they not bother to help you to lure or push back the fireballs.
TL:DR; This build is best to Solo Saalus/Mission, but you need High Transcended weapon to overcome high mdef monsters in lv300+ Map.
Pyro3 -> Linker2 -> Psychokino > Sage
With this build, you can only routine Fireballsx2>Duplicate>10s+>Fireballsx2 = 6 fireballs and Joint Penalty during boss time, not mention the link break on lesser hit count. On the other hand, this build Psychic Pressure is redundant with Hell Breathe, you can only use 1 of a time.
The good part is Swap, you can swap your boss into your fireballs paradise to ensure the right positioning, the fireworks combo is a bit overkill when your fireball can did enough damage.
But the main mechanism should use firepillar to trap them for 10s+, and take your time to setup fireballs and PP them, they do better on link-resist targets.
TL:DR; Fireballs+PP very gimmick to use, not effective on chaos situation compare to deploy and lure.
Pyro2 -> Linker2 -> Thauma2 -> Sage
Also routine Fireballsx2>Duplicate>10s+>Fireballsx2 = 6 fireballs
This build is quite well-rounded that more specialize in farming and good in general, be in solo 240dungeon or crystal mine of any low level mats with JP+HK+Swell Body combo.
In regular mobbing and questing, just put 1 fireball and JP as many targets as possible, the HK and bam monsters will die really fast.
TL:DR; Strong enough to kill regular monsters or Boss without rely high matk weapon, and with better ability to farm. But the maximum potential damage lesser than pyro3-linker3-sage on perfect setup (where multiplication works like crazy and overcame the mdef wall with trans weapon), which can only be done if you are the sole DPS in party.