Hey Humanity, I'm so glad to hear that you're enjoying the game!
Yeah, marksman is a super controversial champion with some people saying it needs to be buffed way up and some saying it actually needs heavy nerfs. This is because marksman is the only 3/3 difficulty champion in the game (see champions page for more) so with a less experienced player it can feel like garbage. However, if you've ever dueled a marksman one-trick with decent accuracy, marksman is a pretty pretty formidable champion.
A few tips to strengthening your marksman:
First, watch your distance from your opponents. Ideally, you want to stay far enough to be out of reach of your opponent's weapon, but as close as possible to give the highest chance of landing shots. Marksman has 20% bonus base movement speed, so you can outrun all champions except for assassin, who has 30% speed. The speed alone means you stand a really really good chance against all champs except assassin. Against assassin, your best hope is to utilize slowness from your arrows to disengage from melee fights.
Second, marksman's crossbow has a really big hitbox, equivalent to the width of its bow. This provides really strong defense and functions as a pretty powerful melee weapon. "Melee marksman" is actually kinda the meta right now. The only things you have to keep in mind are that 1) marksman has slower base spin speed which means you won't be able to block hit for hit and 2) marksman has about as little reach as assassin. Marksman's close reach can definitely be compensated for by making close-range or even point blank shots.
Third, marksman actually got a pretty nice buff on its passive about a week ago, which now gives slowness upon landing hits. This is helpful for 1) keeping an ideal distance from enemies and 2) landing follow up shots because slowed enemies are quite a bit easier to hit.
So there you have it, marksman is not underpowered! If you want more "pro tips", just ask, you'll be surprised how much hidden micro mechanics there are in this game that can actually make a pretty big difference. Anyway, congrats on being the first ever comment and have a nice day :)