You should really try artillery bombardments combined with logistical strikes. Bombarding cost a lot of supplies so you might want to use attack groups of one art div with three or four non-art divs (for a larger unit supply stock). Having multiple such units you could rotate them into the attack and back out if supply level runs low. This may take long but you should be able to do a lot of infra damage, reducing ESE for the enemy units a lot.
It is very helpful to use offensive supplies for Art Bombardement. Use OS and enough Railroad Art and you can crack any defence. Log strikes seem a bit wasted because Art bombardement already does reduce infra. Bombing down the naval base to reduce ESE could be important.