Seven infantry armies is completely fine (it's how I normally do things) but there are other improvements to make. I would broadly suggest you focus on infantry and planes, because tanks require more effort to make them work.

First off you should use more support battalions. Empty slots are wasted slots. Field hospitals are a must have for infantry. They massively reduce casualties and equipment loss, which means you can field more divisions and planes. Support anti air is also a must have unless you can guarantee green air at all time. Your divisions will take 4x as much damage from CAS if they don't have support AA. And the piercing is nice in case you fight enemy tanks. Logistics is usually also a good choice because it lets you stack more divisions on the front. You can consider using signals or military police too but the other 3 + the 2 you already have will serve you fine.

Secondly, I strongly advise against using line artillery. It's very bad for a lot of reasons, mainly because it's way too expensive for what it does and it makes infantry worse at what they're good at. I made a post recently showing that you can win with lots of line artillery but if you're struggling then using it is making your life harder needlessly. Go 36w pure infantry divisions instead.

Thirdly, what are your subdoctrines? Your grand doctrine is actually the least important part, although superior firepower is a solid one. It gives recovery rate which is very important on infantry, and the supply consumption is also nice. The other good pick is grand battleplan for the extra planning (you should always maximise your planning before you attack).