ETA: It may be useful to alternate focusing on concentration vs observation, seeing as you may only be able to make certain observations after developing your concentration to some threshold.

It seems as if there's a few standard approaches here:

• Buddhaghosa suggests entering (the fourth?) jhana and then retreating, after which the mind will be naturally very concentrated, sharp, and ready for insight meditation.
• In contrast, the Samaññaphala Sutta and other suttas suggest entering the fourth jhana and engaing in insight meditation from there, without leaving.
• "One approach emphasized insight practice almost exclusively, feeling that since insight gives rise to the wisdom necessary for enlightenment, this was what was more important. An excellent example of a sutta reflecting this approach is the Sammaditthi Sutta (Majjhima Nikaya #9). Here Sariputta gives a beautiful discourse on Right View. He discussed 16 important topics and ends each topic by saying "When a noble disciple has thus understood [the topic], he uproots the underlying tendency to greed, hatred, the 'I am' conceit and ignorance, and arousing true knowledge he here and now makes an end of suffering." Here enlightenment is achieved solely through insights; the Jhanas are not even mentioned."

I definitely can't enter the fourth jhana at whim, nor do I feel at all prepared for vipassana meditation. But I think this confirms your reasoning that there are many potentially successful approaches to balancing concentration and mindfulness, which might be good to keep in mind.