The myths around alcoholism/addiction are rife.
In my - and many experts - opinion it's not about necessarily how much or how often they drink/use its about how it affects their actions in the areas of their life they need to act responsibly - so parenting, work, driving etc.
In addition in this case the fact he was able to drink so much suggests to me he may well be drinking more/more often than op knows about anyway.
He's also prioritising drink over his parenting responsibilities. That means he's prioritising drink over his child! That's completely unacceptable.
Op as the child of an alcoholic myself I wouldn't be leaving this guy either in sole charge of the child nor driving this child. I wouldn't trust him not to be over the limit. Tbh I'd be trying my damndest to stop him driving at all.
Actually at this point with my own history, I'd be leaving and doing everything in my power to only allow supervised access to the child until he got the drinking dealt with.
"It’s a sad situation because I don’t want to make him feel like a bad father" well he's not a good one!
I strongly recommend you seek support from an organisation experienced in supporting families of addicts/alcoholics eg al-anon because you also seem to have a level of denial - not uncommon though. You love him and don't wan to think bad of him but remaining in denial doesn't help your child, or even your dh.
I'd class him as an alcoholic op. Alcoholic means alcohol dependent,
www.drinkaware.co.uk/alcohol-facts/health-effects-of-alcohol/mental-health/alcoholism/
www.alcoholics-anonymous.org.uk/about-aa/newcomers/about-alcoholism
Some days he can take it or leave it so does that mean he’s not alcohol dependant ?
I would say
A no because other days he CAN'T take it or leave it and those days seem to outnumber the sober days
B once he starts drinking he can't control his consumption
C it's entirely possible he's drinking when you're not aware he is - addicts are experts at hiding their addiction, they are masters of deception.
"Take it from someone who's been where you are now. If he no longer understands that being bladdered whilst looking after a toddler is fucking stupid and selfish, he's not far away from drinking in the morning" also true - it's a gradual development, people don't become addicts overnight there's rarely a clearly defined moment they become an addict.
"and if he drinks regularly then a bottle of wine over an evening isn't a huge amount" it is - this just means he's built up a tolerance - part of alcoholism.