Indeed. And that's what I'm basing this on. From the "Suggested Options" section under "Skirmishing Warlord" in Martial Power 2, I quote:
tl;dr summary of below: The MP2 features tell you exactly what they are replacing, common sense should apply there.
Seeing as you are quoting here:
ARCHER WARLORD
When you choose the Archer Warlord class feature, you lose proficiency with chainmail and light shields.
I don't read anything in the Archer Warlord section about it being able to replace any class trait at all, except for your proficiencies.
Furthermore, the text YOU are stating demands giving up Combat Leader or Commanding Presence is this:
NEW CLASS FEATURES
You can select the following class features instead of another option, such as the ones presented in the player's handbook or martial power. You need not pick the skirmishing warlord build to select these features.
Under this heading is included Skirmishing Presence. Which, by your logic, means that,
because it is under the same general heading and therefore follows the exact same rules as Archer Warlord, that you can select for a warlord Skirmishing Presence and Tactical Presence, using the 'New Class Features' rule you've stated to replace Combat Leader with Tactical Presence, and Skirmishing Presence to replace... well, Tactical Presence.
However, you'll then take notice that Skirmishing Presence tells you exactly what it replaces:
'When you choose a Commanding Presence, you can select the following option.'
This means that under the heading you described, the feature that is replacing dictates what option it replaces. As well, Combat Leader is not technically an option, it's a set in stone class feature. Which also means by your logic, the only thing Battlefront Leader and Canny Leader can replace is your Commanding Presence.
Obviously, that doesn't make sense, seeing as the Insightful Build goes ahead and shows you that Canny Leader and a Commanding Presence option are living side by side.
The only conclusion made from that, then, is that Canny Leader and Battlefront Leader's telling you what class trait they replace (Combat Leader) means only what it says there, that the only thing it replaces is Combat Leader. And therefore, by logical extention, the only thing Archer Warlord replaces is exactly what it says there, your proficiency with shields and chainmail.
Actually, by my math an 18 INT makes hide equal to scale (+7), not plate (+8). Unless you mean that if you also carry a heavy shield, that you're actually as good as someone in plate and a light shield (+9).
1) You're not carrying a heavy shield as an archer warlord.
2) If you're NOT an archer warlord, and you're a one-handed weapon user (no compelling reason not to with a Warlord, unless you want reach), then chain mail + light shield does upgrade to scale mail + heavy shield. Which is better than plate and light shield. AC is the same, but the extra point of reflexes and speed and skill checks is nothing to sneeze at.
3) Edit: My mentioning of plate there was a typo, my bad.