Henderson missed out on a place in one of Gatland’s squads for the three Tests for a second tour in succession.
The second row was considered unfortunate not to figure in New Zealand in 2017 and captained the Lions against the Cell C Sharks in South Africa this year.
However he was again overlooked as Gatland stuck with an engine room partnership of Maro Itoje and Alun Wyn Jones, with Tadhg Beirne (for the first two encounters) and Adam Beard, for the series decider, preferred as bench cover.
Henderson started the Lions’ toughest warm-up game against a close to fully-loaded Springboks side under the South Africa ‘A’ tag a week and a half before the series proper.
However Jones’ remarkable recovery from a dislocated shoulder saw Gatland’s chosen leader return to the tour before the three Tests in Cape Town.
Courtney Lawes started all three matches at blindside flanker despite having limited time on the pitch in the warm-up fixtures while the Lions protected a nagging injury.
“I would tend to agree with that statement,” Henderson told BBC Sport NI’s Ulster Rugby Show when asked if Gatland selected his side based on familiarity rather than form.
“Courtney Lawes, for example, hadn’t played a lot of rugby, was injured going in, missed a lot of rugby, comes in and starts all three Tests.
“Don’t get me wrong, Courtney is a class player and he probably deserved to be playing, but that would lead you to believe that he [Gatland] wasn’t picking on who was on form at the stage, because Courtney had already banked his form from before.”
Henderson was speaking to former Ireland teammates and fellow Lions tourists Rory Best and Tommy Bowe.
The Ulsterman captained his country for a first time during the Six Nations and is expected to be fit for Ireland’s Autumn Internationals after a thumb injury.
He also criticised Gatland’s tactics on the tour, suggesting that the Lions were foolish in trying to out-do South Africa at their own game after the false rewards of a largely uncompetitive set of warm-up fixtures.
“You could play South Africa’s game-plan against the Sharks or someone like that and whenever you get however many points up, you’re winning the 50-50s, the slap-downs become a 50m try and all of a sudden people go ‘well they’re playing free-flowing rugby today’,” Henderson said.
“Before you know it, you’re trying to beat South Africa at their own game. South Africa just won a World Cup doing their own game. They’re incredible at it.
“Falling into what they’re incredibly good at I think is something a team probably shouldn’t try to do playing a team like that.”