The biggest problem is not the odds of landing top 4, it is the fact that after top 4 the order is set by worst record. Now that they have adjusted the lottery odds it is the locking in a floor for their draft pick that is encouraging teams to tank. The best idea I have seen for that is to have several mini lotteries. So first, you give everyone the odds for landing top 3 or 4, with the worst teams getting the best odds. Then, after you pick the top 4 you take the next 3 teams with the worst records. But instead of slotting them in order, you put them in a random, unweighted draw, where they all of 1/3 chance of being 5, 6, or 7. Then you go to the next three teams and do the same for 8, 9, and 10. Then you do the same for the last 4 teams, 11-14.
The beauty is that no one knows exactly what the cutoff will be for each grouping until the lottery actually happens. If no one jumps into the top 4, then the teams drawing for 5-7 will be the 5th, 6th, and 7th worst teams. But if the top 4 positions went to the teams with the 3rd, 7th, 2nd, and 11th worst records, then the draw for 5-7 would be teams 1, 4, and 5. Then the draw for 8-10 would be the teams with the 6th, 8th, and 9th worst records.
So the worst teams still get an advantage at getting a top 4 pick, and the three worst teams cannot fall below 7, but after that it is pretty hard to know what you are tanking for since so much is left up to what happens on lottery day, and teams like Indiana, Portland, and Sacramento would have pretty even odds going into lottery day.