I started last month. Worked my way from rank 50 to rank 19.
Getting to rank 19 was hard! Everyone had such powerful “I WIN!!!” cards and played them again and again and again.
But I made it! Rank 19! I was told that there was end of the month rewards.
I just opened it to find them…my heart pattering with excitement.
I opened the chest and got…
10 dust and a common card.
BE STILL MY HEART!!!
edit - this goes with my first arena run. I went 6-3. 75 gold, 20 dust and a deck pack. Seriously??
It can be considered an achievement depending on how much effort and time put in.
The most important thing is to enjoy life both within and out of the game.
Good Luck and Have Fun
Rank rewards do not worth it past R20.
Arena reward 5+ wins start to get decent but gold amount can be random, in your case you probably got little bit less than average. At 7 wins you get 150+ gold back essentially making your run free.
If you want to consistently be good at Arena start watching Kripparian.
P.S.
Actually 75 gold + 20 dust not that bad. Entry cost 150g. You got Pack (100g) + 75g+20d = 195g return. So you made 45gold 
Continuously getting 5-6 wins is the path to riches
I got rank 12 my first month. Been playing 3 moths. Up to rank 5 the rewards are small I think.
I got rank 4 last 2 months. The rewards are good there. Golden epic, 3 golden commons, only 15 dust though
Yoir first arena run was great. New players average 2 wins or something. I went 4-3 first arema run. Out of 3 arena runs so far only managed 5 once. So you’re doing great.
Also I agree getting to rank 19 was hard… I kept hitting a wall at rank 20 5 stars…
Next wall is 16 to 15, then rank 12 and rank 8…the grind is real