Bell's series by series average since 2012:
2012
3 matches vs Pakistan - 8.50 average
2 matches vs Sri Lanka - 27.66 average
3 matches vs West Indies - 111.00 average
3 matches vs South Africa - 28.80 average
3 matches vs India - 43.00 average
2013
3 matches vs New Zealand - 38.36
2 matches vs New Zealand - 18.25
5 matches vs Australia - 62.44
5 matches vs Australia - 26.11
2014
2 matches vs Sri Lanka - 34.25
5 matches vs India - 42.42
2015
3 matches vs West Indies - 31.00
2 matches vs New Zealand - 10.75
5 matches vs Australia - 26.87
3 matches vs Pakistan - 31.53
In reality, Bell has put together just 2 great series since 2012; the 2012 series against West Indies where he scored 3 fifties in 4 innings and the 2013 home Ashes series where he scored 3 centuries and was the backbone of the England team. There is no denying or downplaying his contributions to that series.
He had a solid start to his Test career, averaging 39.79 in his first 49 Tests. He went on an absolute tear over his next 20 Tests, averaging 81.86 with 8 centuries, when he was in the form of his life, but since then, over his last 49 Tests, he has averaged just 34.17.
That average of 34.17 in 49 Test matches is a large sample size and not indicative of a temporary loss of form.
I only present these numbers so that everyone has access to the same information and to provide context. Sadly, you don't win matches through style points. As Michael Atherton said regarding Gary Ballance during the recent series with Pakistan - it's not about how pretty you look scoring runs, its about how many you score. If it was all about being aesthetically pleasing on the eye - Bell and Vince would absolutely be in my team. But, as you win matches with runs scored and wickets taken, neither would get in my squad for the winter.
Since 2013, top order batsman (1-4) have a collective average of 38.86. Bell's average over this period batting in the top 4 is 29.42 - a whopping 24% below average.
Averages by batsman (1-4) since 2013 (min 10 matches).
Bell is 39th of 46 batsman. It is very hard to discount, downplay or ignore those numbers.