Trueman is very easy, he performed significantly worse away from home than at home, and could easily be argued he was doding those tours consequentially. Steyn sometimes gets a bit of flak for having a little higher home than away Test matches, but the discrepancy for Trueman is almost 2.5 times as big in magnitude as Steyn's (16.86% more for Steyn, 40.3% more for Trueman).
He was, infact, Not.
The English selection policy of the time was a strange one, no one except the spinners were generally a confirmed pick, for example, even the 1930s Pacers never played all the games that were available to them.
O’Reilly 26/26 (100%)
Martindale 10/10 (100%)
Grimmett 28/30 (93.33%)
McCormick 12/13 (92.31%)
Constantine 15/19 (78.95%)
Verity 40/53 (75.47%)
Ironmonger 12/20 (60%)
Farnes 15/34 (44.12%)
Voce 24/58 (41.38%)
Bowes 15/50 (30%)
Tate 13/48 (27.08%)
Even Larwood 9/27 (33.33%) [Credit to Coronis]
The English Selection policy was a strange one and fully believed in resting their bowlers constantly, constant experimentation with their bowlers and therefore so many pacers did not play full games. Trueman however, had even worse luck as throughout his career he was constantly feuding with the selectors and the establishment.
In West Indies 1954, Trueman and Lock were accused to shouting at, harrassing and shoving around the wife of a MCC member and both almost lost their careers to it, since then many stories have come out and implied that the ones responsible were not the Juniors in Trueman and Lock, but the seniors in Denis Compton and Godfrey Evans and they were the one to be all harrassive and shoving around the lady. Trueman and Lock were most likely thrown under the bus to protect the more respected Compton and Evans, and Trueman would miss almost every game for a few years. He also went against the MCC as the MCC had asked the English team to not fraternise with the Windies team which Trueman directly went against, due to his rebellious nature, and befriended Sir Frank Worrell. All in all, a really controversial tour which ended with Trueman forever being soured against Hutton and the establishment and them soured toward him, as he apparently was not racist enough.
He would not be picked to play for a couple years, and the establishment would always drop him the moment they had a chance as they did not remotely like him. At the time, Subcontinent was barely toured and almost never by the top English players, not that they would pose much of a challenge as the Indians were notoriously bad against good fast bowling and the Pakistanis played on matting wickets where I wouldn't really wager they'd have a good chance against any very good bowler. Trueman was always willing to play whatever Cricket he could, so him not being picked for Australia in 54-55 further soured the relations with the establishment.
in 1958-59, he was injured before the Ashes and medicines failed and he was in pain with his back, he apparently took Lemon Juice and Beer and asked to be allowed to play, it's very unlikely that Peter May would've played any games with Trueman had things gone well...they did not go well. England lost the first two games so badly they had to get the injured Trueman to bowl, and they dropped a hilarious amount of catches off him when he got in and the umpiring for this tour was notoriously crooked. All in all, combined with Trueman not being at 100%, everything going wrong for England, the umpiring being notoriously bad even by the standards of the time and mostly important, being an injury influenced series, him not being top form is understandable.
Really, it was in 1960 when he got his first fair dig at the West Indies, dry dead wickets combined with the ruthless batting of Garfield Sobers, Frank Worrell, Rohan Kanhai et cetera. It was pretty much a nightmare series for a bowler, Godly batting, dead wickets, extremely high scoring. Trueman averaged 26 with 21 wickets in 8 innings, was the highest wicket taker, 4 of the games were high scoring draws and only one game had a result, and that was an English victory spearheaded via a fifer by Trueman and him suppressing Sobers, winning the series. The performance was very highly rated at the time, especially when you put it all into context.
By 1962/63, he got his first non injury influenced dig at Australia, his pace had gone down significantly and the series was also very high scoring, 35+ Run-per-wicket and 3 of the games were draws. Trueman won one of the games and was the second highest wicket taker. He averaged 26 and again won one of the games by himself, drawing the series 1-1, he'd retire in 1965.
All in all, I think the idea Trueman was a HTB is a bit overplayed, he was godly at home but his away tours are really rough, one of the tours he straight up wasn't payed for and the establishment almost ended his career, he was not at 100% in 1958-59 and only played because the other English bowlers were god awful and the series is still injury influenced. Then he just got two digs at the two strongest batting lineups on dead flat wickets where 70% of the games would be draws and he'd win 2 of the 3 games that even had a result, by himself.
he only really got digs at elite batting on flat wickets in the 60s, never really got a dig at weak South African battings on spicy Saffer wickets, or the weak Pakistani batting lineups on mattings and so forth. While I get it, He doesn't have away ATG tours so should be below Imran or Steyn or yada yada, I don't think many bowlers are doing much better than 41 @ 26 against the top two batting lineups on flat away wickets. I don't think he was a HTB or whatever, just someone who the establishment of the time despised and tried hardest to get rid of, and someone who was dealt a pretty rough hand away from home generally.
Anyway, that's just my beliefs, apologies if it got too long.