Not a question of guts but just one of having half a brain.
Thats a fair assessment of his career overall. As you said 33 average at 78 strike rate is nothing more than decent. Granted, thats light years better than what you or I or anyone on this forum could achieve.
However, context is key. When judging players today, I like to look at the recent past. In the last 3 years (since the end of the last WC) if we look at batting stats we see where the modern game has headed. I am fully aware that Mushfiqur Rahim averaged 20 at a strike rate of 55 back in 2008. Totally irrelevant to 2018 and beyond.
Kohli leads the way with an average of 79 at a strike rate of 97. Even in today's batting friendly era, with most of the rules going against the bowling side, that is a phenomenal record.
We see that the best international batsman average around 50 at a strike rate of 90+. Have a look for yourself
here
By this standard Tendulkar's career numbers of 45 and 85 would be distinctly ordinary - not to mention pale in comparison to Kohli. But the era's are different and that is the context.
So we see the top 10 by average are:
Kohli
R Taylor
Root
Tamim
Rohit
Faf
Warner
Babar
Bairstow
ABD
Kane Williamson and Steve Smith don't even crack the top 10.
If you look at strike rate, Kohli ranks 9th, but he's still way ahead of Root, Williamson, and Smith. Thus a strike rate rank of 10 is still world class.
Given that information we see that Mushfiq's average is 47 at a strike rate of 90. Which puts him level with the likes of Williamson and Smith. Does that warrant a "at best, above average" tag? I disagree. I would say that is "not the best batsman in the world, but damn good" tag.
Now it might be argued Mushy has scored soft runs akin to say Shahriar Nafees (or Babar Azam). So I looked it up:
Mushy vs top 6 teams
Average actually jumps to 60 at a strike rate of 91.
So then I looked at it away from Bangladesh, since BD can't win outside of Mirpur, ergo you'd expect the players to struggle individually as well:
Mushy vs top 6 outside of Bangladesh
Average skyrockets to 69, strike rate falls, but still a decent 83.
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So my assessment - and I've watched about 80% of career live so its not just highlight reels - is that Rahim from 2011 onwards became a world class batsmen just lacking in consistency. But since 2015, he is in the 2nd tier of ODI batsmen, next to the likes of the Williamsons and Steve Smiths.