The Silverstone outfit made huge progress in 2023, with Alonso logging eight podiums, including three second places.
However, with his team-mate Lance Stroll falling well short of that strike rate, Aston only moved from seventh to fifth in the constructors' championship.
Alonso concedes that the team performed better than he'd expected in his first year, but he's adamant that making further progress won't be easy.
"The starting point is a little bit better than what I thought," said the Spaniard. "But now the real difficulty starts.
"I think the first step – I will not say that it's easy to be competitive – but I think with so many examples, like Alpine last year, is to be sometimes even in the top five or something, when we were in a happy place some weekends.
"We see AlphaTauri, how much they've improved during this season. So, let's say that that first step, to become a top 10 contender, is the easiest part.
"Now comes the tricky period for Aston Martin. I think the next two or three years – to find that extra bit, to create something that no one has in that moment, to be creative, to be innovative, I think that's maybe the biggest question mark that we need to face, and I think no one has the answer."
Alonso says that Aston learned a lot from its experiments with different aero packages in the latter part of the season, and now has a good understanding of what direction to take with the AMR24.
However, he cautioned that the team also has to remain flexible as the sport moves so fast.
"I think there are clear indications of some parts of the car that they were underperforming for a few events," he noted. "They were also different philosophies on the pitlane, but also for us in the way you try to extract the performance of these cars.
"And I think now with all the experiments and all the knowledge of this year, we think we understand better the direction to develop the car.
"But these things are moving constantly – I don't think that there is a magic bullet and a recipe to develop the car. If so, it would be very easy for everyone.
"But things that you maybe think now and trust now, in six months' time because maybe the trend on the pitlane is to maybe move the airflow in a different way, they get outdated and very quickly. So we need to keep an eye [on things]."
Additional reporting by Alex Kalinauckas
