Halo Infinite started development almost 5 years ago, of course it was going to be cross gen. That shouldn't be a problem, the problem is it didn't even look great for a cross gen game. Look at the reaction to Gotham Knights (Cross gen), compared to Infinite. The overwhelming majority of complaints with Infinite were related to its graphics and presentation, elements that absolutely should have been scaleable to the first year or two of next gen. Look at cross gen games from last gen or ones announced for this gen, they still held/hold up in the first year or two graphically while Infinite clearly does not. The whole cross gen issue isn't even an issue at this point anyway, we know the studios choose what platforms they want to release on and the overwhelmingly majority went with next gen exclusive. The problem with Infinite isn't cross gen, people are just looking for something to blame for Infinite's graphics and presentation being sub par. Sub par for even a current gen game, let alone a cross gen game. The problems are quite obviously in different areas, related to 343's planning, scaleability and tech.
Does cross gen development hold back games? absolutely it does. But that is accepted with cross gen games at the start of a generation, as the first year or two you don't see a big jump in either game design or graphical quality. But what people expect is for cross gen games to still hold up well graphically in that first year or two, which they usually do. Infinite being cross gen doesn't prevent it from possibly being an amazing game obviously, Switch's lack of power in comparison to last gen didn't hold back BotW from being an amazing game. But there is no excuse for Infinite looking the way it does.