I don't think it's outdated, it just isn't all that good. If you ignore the wild peppers, steps 1 and 2 are generally fine. Purple corolla isn't exclusive to pubescens, but pubes have a look one can generally get familiar with. Step 3 should probably be chinense referencing annular constriction of the calix with more than 2 flowers per node being a secondary indicator. Separating annum and frutescens can be more difficult with the upright fruiting annuum types, but starts with flowers upright, nodding at anthesis, with greenish tint versus true white and 1 or 2 flowers per node being secondary considerations. The wilds will create overlap with baccatum on color-spotted corollas as will, less commonly, frutescence. Also, with pubes as to dark seeds and flower color. There's considerable overlap with respect to flower parts in general, such as filament and anther color, etc. Other traits overlap as well. Some annuum will cluster flower.
I've never seen one very good source with a short presentation identifying everything neatly and there will always be exceptions. The above are the broad indicators though that will get you there a very high percentage of the time if you know them all, but there are some curve balls. There are entire research papers on localized drift in frutescens characteristics and the like. Wilds are likely where you'd need to get most into the technical features such as calyx teeth and the like as necessary for ID purposes.
There's also an art to it. How do you ID a pubescens that's pre-flowering if all you're looking for is purple flowers and dark seeds? Or a baccatum that hasn't flowered? Etc. Leaf shapes and textures, growth patterns, other things you get familiar with help here. Again though, there's always going to be stumpers, especially with younger plants with fewer defining characteristics present. Heck, the experts even argue and change classifications from time to time.