Problems with Comparatives

I believe I am correct in saying that the example sentence below is incorrect because of the word that I have written in capitals. Below this, I have written how the sentence should be correctly written - which contains the correct replacement for the incorrect word, again in capitals - but can anybody tell me WHY it has to be said like the second sentence and not the first? Is there a specific grammatical reason for this? "Lazio earn LOWER than 50% as much as Barcelona" "Lazio earn LESS than 50% as much as Barcelona" As far as I can see, both "lower" and "less" are comparitive forms of the adjectives "low" and "few" respectively. Am I even correct in saying this? (NB After having written out this question it has actually occured to me that the answer may have to do with the word "percent" being usually written out as a SINGULAR noun, rather than plural. We say "50 percent" but we MEAN "50 percents"; so in effect, it would appear that we are using a number to describe a 'quality' of a single thing - rather than to say HOW MANY of those single things we have. I suppose this is similar to the way that we talk about the age of a human being: we say "I am 50/ She is 32" etc, not "I have 50 years" or something like that. We can use a word like "low" to describe a quality of a single thing; but we use the word "few" to describe how many of a certain thing we have - similar to the different possible uses for a number, like "50". Therefore, it follow that we don't use "lower" in the example sentence - since we are talking about the NUMBER OF percents - we use "fewer". Am I on the right track with this?....Please help if you can.