No. 4e was the least challenging for characters.
If you find 5e too easy, first make sure you are following the 6-8 encounters per day. If you want less encounters use the slower healing options of the DMG.
In short 5e is expected that you normally have 6-8 lethal fights for the party
per day to challenge them. You're going to be depopulating entire towns at that rate.
As for 4e not being challenging for PCs, I think I've killed PCs more regularly in 4e than in any other edition. On the other hand every time I did I was able to look back and say the PCs had made a mistake somewhere (I normally spotted it at the time). In every other edition PCs have normally died not because the challenge was higher but because the dice hated them that day.
And
@Sabathius42 a better way of looking at it would be which of the following four mutually exclusive choices is "less challenging"
A: All PCs may access 100% of their total hit point pool at any point in the day whenever they need it (TSR era). GMs are expected to produce low threat encounters in order to whittle away this pool without seriously threatening the PCs
B: All PCs may access 100% of their hit point pool at any point in the day. PCs who aren't first level have easy access to items like Wands of Cure Light Wounds to top that hit point pool back up to maximum on short notice. In order to make up for this save-or suck spells frequently dominated. GMs are expected to use 4-5 encounters/day to properly challenge PCs.
C: All PCs may only access about 33% of their daily hit point allowance at any given time. In an emergency instead of attacking they could draw from their daily pool at the cost of giving up their attacks for a round (which is almost always not something you want) - and hit point recovery that does not draw from this daily pool is extremely rare. GMS are expected to produce high threat encounters that challenge this short term pool although multiple in a day is good to challenge endurance as well as short term.
D: All PCs may only access about 50% of their daily pool at any given time but hit point recovery that does not draw from this daily pool is common. In order to properly challenge PCs because they have fairly deep pools GMs are supposed to soften them up by using 6-8 encounters per day.
And this is why I consider that with good GMs (and using MM3 math) 4e is the most challenging version. You can run the PCs far closer and far tighter without fudging because the slings and arrows of outrageous fortune are reduced and you have a much clearer indication of both how the PCs are going to be at the time and what your monsters can do thanks to much better balance. oD&D was a "test your luck" game for the challenge in part - 4e is a "good movement tactics" game.