I agree with all of this and again will say the warlock frame would make a better fighter.
At 1st level choose half your sub class (instead of patron this would be eldritch knight for example) at 3rd you would drill down a bit more with second half of sub class. You get a good encounter/short rest recharge of abilities that can affect both combat and non combat (like the 2 spell slots) and every couple of levels you can pick up either daily or at will abilities (like invocations)
Sounds interesting. Have you given it a go?
This was also the idea I had, should I ever sit down to write a Warlord for 5e myself. I decided to make a Summoner instead (which, ironically,
also uses the Warlock base--because Invocations are perfect fodder for "elective boosts you get a finite number of"), which is about 25% done, so it's nowhere near complete enough to properly share.
At least for the concept stage of the Warlock-style Warlord, my idea was:
1st level gives you your Leadership Style, which determines your Leadership Modifier and provides a set of baseline bonuses. E.g. Resourceful = Wis, gets more out of healing & extra uses of actions; Tactical = Int, gives initiative and movement buffs; Bravura = Cha, high-risk/high-reward play.
It also gives you Feints and Stratagems: Stratagems are more powerful (and generally more aggressive), but require a resource--Gambit--which is earned by your allies taking damage, or through successfully employing a Feint, so you have to "earn" Gambit to "spend" Gambit.
2nd level gives you Tactics, a collection of passive effects, one-off triggered effects (think "Fastball Special"), and at-will actions.
3rd level gives you your Strategic Focus, which is diverse and opens up new Tactics to exploit. E.g. Mage-Captain lets you do things that improve allies who cast spells, Battle Medic gives you great healing, Vanguard gives you the defenses to stand right in front, Skirmisher makes you part of the back line firing volleys, etc.
My only real sticking point was needing to find something really meaty to replace the normal Warlock Mystic Arcana with. Perhaps "Grand Stratagems" or something? Not really sure, never sat down to really give it the thought it needed.
Have you played it? Everyone I hear from raves about the in-game tactical choices and part synergy required. It is one of the reasons I am hesitant to give it a go myself! Now, it is much more deadly than 4e, so maybe that is not your thing (I think it was you that wanted characters to be heroic from the get go, but I could be wrong)
I have not, but I've heard exactly the opposite: that it flattens the strategy out. Which made me lose a lot of my interest. Would you have a link to something that says otherwise? I'm certainly willing to give a second look. (After all, I originally had to give 4e a second--and third!--look before I realized what it was really offering me.)
The fact that the "Synthesist" Summoner they offered (for playtesting) was...really really not good, as in "spending a resource to be
worse than you were before" not good, definitely also dampened my spirits, unfortunately.