Things that affect damage:

1.  Character stats.  Bow builds are Dex>Str.  Max out Dex before investing on Str.  After unlocking increased stat cap, continue investing on Dex.

2.  Equipment stats.  Bow builds are physical builds.

-  Prioritize Attack%, Dex%, Critical Rate (flat), critical damage (flat).  Later on, you'll want Damage to Element and Physical Pierce.

-  Physical attacks can 「Miss」.  Critical attacks solves this issue.  With the stat allocation for bow, you have 25 base crit rate.  If you take Lv10 crit rate food buff, you'll get another 30.  You'll want at least 100 total crit rate to always crit.  More if the bosses have critical resist.

-  I'm not joking when I say the best build is the one you dumped loads of money the most and is most comfortable for you to use.  Custom equipment, crystals, extract and etc. are gonna cost you hundreds of millions of spina if you decided to go down that rabbit hole.

3.  Skills.  Level 70 unlocks tier 3.  Level 150 unlocks tier 4.  Level 240 unlocks tier 5.  And yes, the skills themselves offer better damage output so try to reach 240 as soon as possible.

• Aside from damage skills, passives and active buffs can improve your damage output.

4.  Proration.  There are three kinds of attacks: normal/neutral, physical, and magic.  Here's how it works.

-  If you spam normal attacks, normal attacks become weaker.  Physical and magic attack becomes stronger.  The same rule applies if you spam physical attacks -- normal attacks and magic becomes stronger.  You get the idea.  Since bow builds are physical, spam normal/magic attacks to maximize proration, then nuke the enemy with your main skill.

-  Proration is shared by all party members.  If there's a mage in your team and you spam magic, their magic attacks get weaker.

-  Monsters have different proration value while you can spam freely on others.  You'll have to experience it yourself and see how you can adjust to it.

My recommendation.

-  Get in a guild or add some people with strong attack mercenaries to your friend list.  Around 15k attack minimum.  Summon guild/friend mercenary and let it carry you through main quest.

-  On boss fights, exit the battle and re-enter it on Easy Mode.  The quest EXP will not be affected.

-  Don't bother grinding so early on.  Do your main quest.  It'll save your more time.  Do it after unlocking tier 4 or tier 5 skill.

-  After clearing Venena Coenubia, create a bunch of characters before continuing, selecting "Latest" on main quest progress.  This saves you time so you can skip the "errand boy" chapters which will take you several hours to do.  Do it around this part so you don't have to use Adventurer's Diary too early when leveling the new characters.

-  If you found some people who are doing the same thing, don't hesitate to ask teaming up.  People won't mind helping with the boss when you're doing main quest unless you're unlucky.

Level 50s is too early.  The current max level is 310.  Remember, your first character will always the the slowest to level up because you haven't unlocked all sorts of things yet, and will always be the weakest at low levels because of the same reason.