A run rate of 10 runs per over is not really impossible to achieve for the teams in T20I cricket at all, thanks to the modern day bats and also to the audacity of the modern day players.
In some cases, the size of the boundaries helps as well, as the organizers at a lot of venues shorten the boundary size deliberately to allow a lot of big shots.
Here are the teams with most 200+ scores in T20I cricket –
#1 India (17 times):
India has posted scores of 200 or more runs 17 times in T20I cricket so far and this is actually an eye-opening stat for some of the critics who believe that the Indian batsmen often slow down in the middle overs of a T20I innings and approach it more as an ODI game than a T20I game.
This criticism is somewhat fair when India bats first, but not when they bat second. India, as a chasing team, goes through its gears properly.
Seventeen scores of 200 or more runs clearly suggest that India has got the firepower in the engine room when it comes to T20I cricket.
#2 South Africa (13 times):

South Africa has struggled a little bit in white ball cricket of late, but they have had some real power-players in the past who made a lot of impact for them, both at the top as well as lower down the order.
Quinton de Kock at the top of the order and David Miller as a finisher are currently the two power-players in the South African line-up and if AB de Villiers is back at no. 4 (as speculated), South Africa might be back as a potent batting force in the shortest format again.
South Africa has posted 13 scores of 200 or more runs in T20I cricket so far.
#3 Australia (12 times):
Australia has not been able to win the T20 World Cup so far, but they have always had a very decent T20I side. It’s not easy to beat them in the shortest format at all, given the kind of batsmen they have got right through their line-up.
Most of the players, who are a part of the Australian T20I side at the moment, are the most sought after names in the T20 leagues around the world as well. Whether it’s Aaron Finch, David Warner, Glenn Maxwell or Mitchell Marsh, all of them are capable of hitting a long ball.
Australia has crossed the 200-run mark 12 times in T20I cricket.
#4 New Zealand (9 times):
New Zealand probably has the smallest grounds in the world in terms of the dimensions. Some of the other countries also have small grounds, but in New Zealand, there are a few venues where you don’t have to hit the ball any further than 55-58 metre to get six runs.
There is hardly any low scoring T20I game in New Zealand unless the pitch has something in it to help the fast bowlers get early wickets.
Because of the dimensions of the New Zealand ground, if there is nothing in the pitch, 200 is a par score most of the time.
New Zealand has scored 200 runs or more 9 times in T20I cricket.
#5 England (9 times):
England currently sits at no. 5 in this list, but the way they are playing in white ball cricket these days, they will move up this list very soon. They are one of those teams which don’t drop their guard at all at any stage of a T20I innings, doesn’t matter if the field is up or the field is spread.
They look to accelerate all the time and in the process, even if they lose wickets, they don’t go into their shell for a long time. England’s approach to T20I cricket is probably the best among all teams.
England, just like New Zealand, has also posted 200+ runs on the board 9 times.