Part of this is not just found in the Warlord class, but also in the Fighter class. In 4e, the Fighter was a Defender – or a tank, in MMO parlance. They could take a lot of damage, and dish out OK but not amazing damage, and penalize enemies for attacking their allies. The 5e fighter is a much more generic class.
The Warlord was a Leader, although I think it would have been better to use Support. They heal, buff, remove conditions, "shield" via temporary hp, and move allies into position. So they fill a very different role than a 4e Fighter.
However, even ignoring that I do not think 5e works very well for a 4e-style Warlord, because many of their abilities relied on specifics of how 4e worked:
- 4e assumed you were playing on a grid, and positioning on that grid was pretty important in order to gain flanking/combat advantage, fit things into smaller AOEs, and so on. 5e by comparison does not assume the use of a grid, and does not have many abilities that depend on positioning (e.g. flanking). So moving allies around isn't as useful.
- 4e healing was based on healing surges: batches of healing equal to 25% of your max hp, of which you had a limited number per day. Almost all healing in the game was in the form of "spend a healing surge", possibly with an added upside. Since the healing scaled with your actual hp, it was always relevant. In 5e, you instead have Hit Dice, which stay the same in power but you get more of them as you level up. So an ability that lets you spend a healing surge will always remain relevant, but one that lets you spend a HD will pretty soon become fairly useless.
- In 4e, almost all offensive abilities were attacks. If a wizard cast a fireball, they roll an attack against each target in the area. This means that an ability that gives an ally a bonus to attack rolls will always help that ally. But in 5e, most spells use saves, so unless your wizard buddy is planning to cast fire bolt instead of fireball, a +2 to attack won't help them.
- In 4e, most debuffs and persistent damage effects were "save ends", which meant that at the end of each of your turns you would roll d20 for each such effect, and on a 10+ you got rid of it. So condition relief mostly came in the form of letting an ally roll an extra save out of turn. But in 5e, most debuffs have a fixed duration – some do have a "save ends" clause, but that uses the same save as when suffering the ability in the first place.
