There's a reason why the game introduces you to the Igni spell. It can help with a variety of things such as stunning the Leshen or taking out the group of Jagras. When it comes available, might as well use it to help with any situation. Also when the Jagras stop by, it is best to deal with them immediately since like you said, they can interrupt you from your attacks and let the Leshen get in a good hit or two on you. That said, pay attention where the Leshen is when it teleports since if it is far away, it will likely use the birds or its roots to attack.
Also if you didn't do the Pukei Pukei side quest, it probably would be in your best interest to do so just to help the last part just a bit. Other than that, it is all a game of patience.
As for the bow, I can't say since I've done the hunt with LS, hammer, lance and Geralt's Silver Sword &Not Shield. I feel like even though the Leshen doesn't move around much, it can still tank attacks a hell alot better than other monsters in the game (but that's just me).