Beeline Steel with Oromos is maybe even stronger than going to Rifles first, since it gives you more edge. Also, paired up with support from Maces which I amass before hand with CR1 and 2 is really good, and than I usually upgrade those to Rifles.
Going for steel before rifling is something I find better in almost all circumstances whether I have Oromos or not!
The problem is that I'm not used to build Muskets or equivalent since it always looked to me that they have short spam of time where you can use them effectively but these guys are changing my opinion on the whole matter.
Muskets are quite underated imo. They have a decent strength value, but the most important aspects are that they are draftable and lie on the path to steel.
Oromos in particular are very good for drafting, drafted uniots only have 1/2 the normal xp in a city, which doesn't affect the 2 free promos, AND Oromos are immune to first strikes which is great against the longbows you will likely face.
Steel and draft will go a very long way with how amazing Oromos are
My initial question was about Drill itself is where does it give you more edge? My opinion is attack since the Oromo would be on par with longbows in strength level roughly speaking, where having Drill on defense is a waste since it can only shine in the part of your land where you expect an invasion, right?
First strikes from Drill best when you have a strength or health advantage. So these situations really.
-If you outtech your opponent by a decent marging Drill helps attacking with a good chance of taking no damage,
-If you have defensive bonuses (city or field!) then it will give a good chance of no damage to the defender, which is very important. It also greatly reduces collateral damage from enemy siege.
-Attacking wounded units is obviously a good plan in any case, but Drill gains directly from the loss of an enemies hp whereas other lines only gain by the loss of strength, this is a wierd concept so i'll post an example
Drill 4 Oromo against a full health 14
rifle
Well this one was obvious really
Drill 4 Oromo against a 52% health 15
infantry
Strange though it is, the 15
infantry is odds on losing against this 9
Oromo thanks to low hp and first strikes
This hp thing is something that isn't worth worrying about unless your behind in tech though.
There are 2 significant drawbacks to Drill promos however, first is some units are immune to first strikes (mostly mounted types) so be careful of that, and the second is that the first 2 Drill promos are very weak while 4 holds most of the power of the drill line, this makes it less attractive if your leader isn't protective or has a UU with Drill 1