Eddie Hackett was the catalyst for bringing golf to numerous communities (with little or no development budget) after the sport exploded in popularity in Ireland with the 1960 Canada Cup. For that, he is rightfully revered right through the island.
Could his designs have been better? Well, as Tom says, he used the natural land very well (he had an aversion to changing it). His routings are very good. I’m sure that in many cases, there were better solutions out there. He did route occasionally awkward looking holes.
He did not have an eye for strategy in his hazard placements. Generally speaking, he wanted bunkers placed as guidance rather than to materially affect the decisions on how to play the hole. He also (through budget or just lack of presence) did not seem to prioritise construction detail. In most cases, locals were left to build the courses but Eddie certainly did not insist or have the inclination to prevent some of the very artificial / rudimentary shaping.
So sure, his courses could have been better. But because he did so little, and despite - or maybe even because of - the basic construction where he did move earth, his courses are very difficult to date to any particular era. And that holds a lot of weight with me on links land. Almost every modern designer (most with considerable more skill at their disposal) has gone on to do “too much” with linksland, therefore dating their course to a modern era.
For this reason, we should herald his designs. They could all be “improved” in many areas but better to be a little reserved in suggesting these improvements lest you end up modernising.
In the end, I want any links course I work on to hide the “design / artistry”. It’s way too easy a landscape to go to town on.