I think the issue comes down to mismatched communication styles. I have friends who are constantly on their phones and others who go weeks without glancing at them. From what you've said here, there's nothing wrong with this guy's conduct and the signals he's sending you suggest he's keen and committed.
For whatever reason, messaging is a big thing for you and you expect that as some sort of baseline of commitment, just as someone might expect a kiss hello or a bunch of flowers to be sent once in a while.
You're not wrong exactly to want this. Your expectations are what they are. And its certainly good to be aware of what feels wrong to you -- that's a sign of good boundaries.
But I think you do need to ask yourself if you are being too fixed in your expectations over something which is frankly rather trivial and whether you are setting a bar for him that is unrealistic or just irrelevant.
He clearly isn't a messaging person. You're within your rights to expect him to be kind, considerate, attentive, truthful and affectionate and to prioritise you but I don't think you can really expect him to totally reevaluate habits and lifestyle points that have nothing to do with you.
You clearly have to decide if whatsapp and text messages are a hill you want your relationship to die on. Personally I wouldn't leave an otherwise strong and happy relationship over this I think its a side issue and you would be much better off reframing this so you accept that its something he won't do. In the long run you will come to realise that text messages and WhatsApp can actually be fairly superficial markers of someone's affection for someone else.
But if it really is that big a deal you may have to move on.