There are too many variables: people, machines and different points in time. It's too early to point the finger at the machine.
I'd say give it more time to develop your technique, and to adjust to the increased power of the boiler. Your Delonghi probably had a thermoblock heating system which is much slower (weaker steam pressure, lower steam temperature) than your Isomac.
I jumped from a Sunbeam to an E61 machine about a year ago. It took me about 2 weeks before I was able to get a decent milk. It then took another couple of months for me to get perfect microfoam.