This is a Player Damage build I have been using for hard mode tower bosses. The build involves dealing massive weak point damage while staying alive with Felbat and Life Steal.

PALS

Vanwyrm (regular & cryst): 90% player damage bonus to weak points. Aerial Marauder should not stack, but somehow it does after testing.

Cryolinx Terra: 60% power bonus after hitting enemies' weak points continuously. Works best with automatic assault rifles.

Solenne: 80% player ATK bonus with a team of unique pals. Way better than stacking 4 Gobfins.

Felbat: Combat pal with Life Steal. Provides healing whenever we or it deals damage to enemies but it must be active on the field.

PASSIVES

Vanguard & Stronghold Strategist for player ATK & DEF boost, Reload Master for faster weapon reload times, and Idiosyncratic for player HP regen. For Felbat, I went with Immortality for extra life steal & pal HP regen, and Sanctified Meat Shield for extra DEF.

WEAPONS

Plasma Rifle & Drone Launcher for DPS, Mechanical Bow for burst damage, Laser Sword as backup weapon, and Pal Recovery Grenade if Felbat's HP gets very low.

ACCESSORIES

Attack Pendant & Dogen Emblem for player & pal ATK boost, Warsect Terra's Belt for player HP & DEF, and Silvegis Emblem for player & pal DEF.

HARD MODE TOWER DIFFICULTY

After testing this build, the only boss that the build struggles the most is Auri & Shaolong (#8), as Felbat is weak against them and they constantly spam AOE attacks that hit absurdly hard. Wing Pack is a must here to quickly evade such attacks.

Another boss that can be somewhat challenging is Victor & Shadowbeak (#5), with a high HP stat and packing strong attacks. The clone it summons at ~25% HP is also something to look out for, but can be countered easily (the real boss does not have a HP bar above them).

The rest are easy as they usually move slow and have predictable attacks that are easy to dodge.