I'm happy with him as our #9 going into next season. For me, he's not only been our most consistent attacker, but has been our best player in general this season.
One thing that shouldn't go unnoticed that he displayed this season as a CF was his versatility in the position. Pre Bruno (& Pogba coming back), he was playing as a false 9. He had to do this because we lacked the players capable of getting the ball to him on a consistent basis, so he'd constantly have to come deep to create for himself and others. He was brilliant in this role.
Then, after signing Fernandes (&, later on, Pogba returning), he started playing like a classic 9 because we actually had midfielders capable of getting the ball forwards now. He was brilliant in this role, too.
There aren't many CFs who can play both style of 9 to the same level as him.
Regarding his stats, they're impressive in and of themselves. Especially when you take into account that he missed two months of the season, was playing as a CF for the first time on a consistent basis in his senior career, and was playing with only one player on his level for about half a season.
In the Premiership, he was joint first with Raul in assists for CFs, and when you look at some of the huge chances missed this season, he could've had more. His throughballs to onrushing FBs/wingers when deep shouldn't go unnoticed either. They were key to many of the chances created in the earlier parts of the season whilst playing as more of a false 9.
With his goal tally in the league, some might see that he didn't reach 20 and assume he can't do it, but context is needed. First, he was hardly getting chances in the first half of the season due to our poor creativity. Then you need to factor in the two months he missed. You then have to remember that, unlike most of the other CFs in the league, he doesn't take penalties. When you look at just goals from open play, I believe he was the 3rd top goalscorer in the league this season. If, like his CF counterparts, he took pens, he could've probably won the golden boot considering we got 14 of them, was it?
Ability wise I think he's one of our most talented CFs ever. A lot better than Saha, and that's no disrespect to Saha who was talented. That's not to say I think he's already one of our best CFs. I'm just talking about ability alone as per your own statement.
I'll finish off by saying that along with his physical talent, I think he's one of our most mentally strong players, too. There are a load of examples of this, but you can just look to recently to save time. When Pogba, Fernandes, Rashford and Greenwood all looked shattered/done at different points of our last few games, Martial was the one constant who was constantly playing well; keeping us on track for that 3rd spot we won.