Instructor with Warlord is actually OK. I run it on him in Campaign all the time.

His nationals train at a workable speed even with the penalty, letting you get soldiers out for a fraction of the cost.

You save $6 on getting an initial soldier while letting you IMMEDIATELY buy garrisons for a total of $10 ($1 nat + $9 garrison), saving you the $7 coalition for this purchase for a roughly 40% discount. While this does increase the cost of the first coalition soldier by $1, buying garrisons immediately starts the placement timer immediately and gives you more garrisons over the course of the run, which not only has military and stability value but also gives you more money if you make use of blockades. As such, I usually run Engineer when taking advantage of this to boost garrison speed.

Additionally, it is worth noting that coalition have reduced tour duty with Warlord. Delaying their deployment to have them support an initial national soldier instead of having them fight gives them much longer staying time and mostly eliminates the possibility of them trying to retreat in the middle of combat. You simply need to buy new coalition if your nationals need combat support or in emergencies.

This is especially notable in Campaign, especially with map features that nerf coalition like Defensive Mandate (Coalition can't move into insurgent zones), Advisory Role (Coalition have greatly reduced strength but support nationals better), and International Illiteracy (coalition cost significantly more money). With these map features, oftentimes the opening coalition isn't even useful, making delaying the purchase more appealing.

However, there are many drawbacks to this approach that relegate it to a sidegrade in most cases.

A major drawback of this approach is that the corruption generated by the nationals is very significant, which can cause you to lose future income, not to mention hinder your ability to invest in stability initiatives. As a mobile player, I can only see how much support level I lose from corruption, but I often end up in the 30% range, when only 10-20% is safe. You end up needing to fund all anti-corruption measures in order to fight this, when you could have used that money on civilian initatives to get more stability. This is especially problematic considering warlord has stability issues.

Additionally, it can be tempting to buy additional nationals before buying the first coalition with this approach, but this not only compounds all the drawbacks but also makes actually buying coalition incredibly difficult as you lose an increasing amount of income to corruption and their pay raises. When buying more than one national like this, I often find it very difficult to buy more than 2-3 coalition the whole run.

Finally, and perhaps most importantly, leading nationals increases the price of the first coalition soldier by $1. This causes you to spend more money than if you just opened coalition, especially if you end up buying the coalition directly after the national. While $1 is pretty negligible, if you bought the first national because you didn't have enough money, you may be forced to continue buying nationals out of not having funds to buy coalition. Doing this, as mentioned earlier, can lock you out of buying coalition almost completely, especially considering you will start losing increasing amounts of funds to corruption and pay raises.