I agree that assists alone does not tell the whole story here and I obviously also had in mind all the times I've watched him play where - sometimes - I've found him frustrating in the final third. His crosses being the biggest issue for me, even when not under pressure, he has showed a tendency to hit the first man in defense - a lot like when Gerrard hit our corners which we also criticized him for (I know I did at least, even though he's probably one of three of my favorite players of all time).
I get your Matip comparison I just don't think it's completely valid, as CB's especially in Klopp's system are not supposed to be involved in attack as much as our full backs, not even close. Full backs ARE an attacking outlet hence why the description 'bonus' for me at least is not suitable when it comes to their attacking contribution. We need them to contribute and deliver in attack as well. I guess we might simply just disagree here, but when I look at a FB's potential I am just as much considering his ability going forward as much as anything. He need the right balance.
Moreno is a good example of a FB that's very good at bombing forward but is equally inept at defending, why he's not really an option to consider until that part of his game comes together. FB's of old were not expected to be as involved in attack as they are today, and Moreno would be called a winger back then, but in today's game and especially when looking at FB's at the top teams there is an increasing need for them to be equally adapt in attack as in defense. Clyne will hopefully get there - as many has said he seems to have all the right physical and mental attributes to do so, so it's a matter of time.
PS You gave me a slap over the fingers because of my mention of Kyle Walker but for me he's at least on par with Clyne and marginally ahead of him too (because of his contribution in the final third). Walker is not Mr. Reliable in the same category as Clyne but far more a threat when going forward, he's got an insane burst of pace, can take on defenders and is extremely strong man to man. I get it why people don't like him as he seems very arrogant but I think it's weird if you don't appreciate him as an attacking FB. Rose as well. I am almost certain they'd both be picked ahead of Clyne and Milner if they were Klopp's to chose from - but that's another discussion.