If we are talking purely about his Test career, first of all, to answer this question, let's look at his career Test stats as of Thursday 29th December 2022:
David Warner - Test Career (still playing)
Home
Matches: 54
Innings: 94
Runs: 5129
Average: 58.95
Highest Score: 335* vs Pakistan, 2019
50s: 14
100s: 19
50+ Scores: 33
50+ Scores Ratio: 50+ every 2.84 innings
150+ Scores: 6
Ducks: 5
Strike Rate: 73.24
Away
Matches: 46
Innings: 89
Runs: 2993
Average: 34.01
Highest Score: 145 vs South Africa, 2014
50s: 20
100s: 6
50+ Scores: 26
50+ Scores Ratio: 50+ every 3.42 innings
150+ Scores: 0
Ducks: 7
Strike Rate: 68.33
Total
Matches: 100
Innings: 183
Runs: 8122
Average: 46.41
Highest Score: 335* vs Pakistan, 2019
50s: 34
100s: 25
50+ Scores: 59
50+ Scores Ratio: 50+ every 3.10 innings
150+ Scores: 6
Ducks: 11
Strike Rate: 71.35
1000+ Runs in Calander Year: 2
Most Runs in Calander Year: 1317 (2015)
Average Runs Scored Per Year: 676.83
Now based on his pure numbers in Test cricket, you'd say "Gee pretty impressive career". However dig a little deeper and you'll see that he is at his best in his home country of Australia. Collectively his technique isn't good enough away from the comforts of home especially in India and England where the ball is alive and does things. In a stronger era of Australian cricket - he isn't playing for Australia in Test matches and in a stronger era of world Test cricket, he would struggle. To only average 34 away from home (compared with his home average), is poor really and not good enough. He is still a good batsman but I have him behind other Australian opening batsman: Matthew Hayden, Mark Taylor, Justin Langer and Michael Slater. I even rate Simon Katich as a better Test batsman and Test opening batsman than Warner.
So overall, good Test batsman, but that's all he is in my assessment.
As for ODI and T20 cricket - very good...why...because that's probably his main arena - aggressive batting.