It's extremely easy to beat the efficiency of photosynthesis since plants are so inefficient. The highest estimate I have seen for carbon sequestration by trees is 7 tons of CO2 per acre, which doesn't include losses from converting wood to biochar for long term carbon capture. Direct air capture of CO2 requires about 2000 KWh per ton of CO2. An acre of solar panels produces an average of 357000 KWh of electricity per year. That means that direct air capture is at least 25x more efficient at converting solar energy to captured CO2. That efficiency is important considering the scale at which we will need to sequester carbon in the next few decades. Cost efficiency is a different matter, but even then I believe direct air capture will beat biochar very soon if it hasn't already.