Yes, when compared to AD&D, 5E is more complicated. AD&D has: no subraces, no subclasses, no feats, no skills except thief, no bonus actions, no concentration, etc. Both have multiclassing, but the AD&D version is simpler. Death and dying is simpler in AD&D. Spells are simpler in AD&D. Resting is simpler in AD&D. The perceived complexity of AD&D is mostly due to optional rules almost no one used like weapon speed and weapon vs armor charts. The only things 5E does that are simpler than AD&D is AC and dis/advantage.
You have a very weird view of complexity if you think most of those are less complex in AD&D than in 5e.
Races - AD&D very much does have sub races, several of which top out at different max levels in the same class and many of which have oddball abilities that need to be calculated or are highly contextual and integrate weirdly with the surprise rules
Skills - yeah, the core doesn't, but NWP appeared later in 1e and added quite a bit of additional complexity
Concentration - it's different, but it sure was there in the way that it could be disrupted when spells were being cast which had a very complex interaction with initiative
Multiclassing - in 5e, it's a bit weird, but 1e's was very complex too. How many hit points do you get? How does each class ability interact with the abilities of other classes - many of which weren't well spelled out
Death and Dying/Resting - 1e's dying was weird, if taken below 0 but up to -3, you're dying (very specific window, that), anything lower you're apparently just dead - so sometimes you get to -10, sometimes not. Then you've got recovery after a coma, and a week of light activity. Meanwhile, characters who didn't get that low recover different rates depending on how many days (and their Con mod) they're resting. That's SO much less complex than regaining all your hit points/half your hit dice overnight.
And then comes combat, which is considerably more complex in AD&D even without the bonus action - weird rates of attack, arcane rules about closing and missile exchange, oddball surprise rules, combat matrices that all vary between class groupings, lots of AC variation depending on attack route, shields, and helmets.
5e is
SO much easier to teach players than 1e ever was.