I have an idea to use. As you know, amount of divisions what can be sent to any given country as expeditionary forces or volunteers are limited. So, if numerical amount of divisions are limited, what about making these divisions as strong as possible? Basically send tanks or some kind of heavy mechanized divisions. And if those are not available, then make huge supported infantry or mobile divisions of maximum size allowed. Yes, they are weaker than several smaller divisions for the same cost, but they are stronger than small division 1v1, and limiting factor there is division number - in other words, cramming as much forces in every division. Is this tactic worth it?

For speedruns not really, since there is very little actual combat and not enough time to gather the needed equipment and army experience for template changes. But during mid or lategame, especially as a minor nation, it's always quality over quantity.

What about this idea, but more simple: just make enormous infantry divisions? They will be stronger than 1 normal division, but weaker than multiple normal divisions for the same cost. That applies to normal playthroughs.

In speedruns i most commonly see using tiny, 1-battalion divisions made of mobile units (mostly Cavalry). These are used to capture territory faster when there is no meaningful resistance - such as flanking enemy divisions and going deep into enemy territory, or initiating Order 66. On the other hand, they would probably be weaker in direct fight than normal divisions. Or not (?) - they would have bigger stats like organization and other things than normal would, so technically group of tiny divisions is stronger than normal division of same cost. But controlling them in normal play would be very difficult - for both Field marshals (they have limit on number of divisions they can effectively control) and the Player himself.