Numbers are an indication of performance. Pictures only say something about how well someone can make that lens perform.
I read plenty a review (with pictures) about the Tam 150-600mm and they ranged from splendid to crap at 600mm. I can look at pictures all I like but a picture usually depends upon the "cam + lens + user + skill + processing" combination. Now I got and shot the Tam, I wonder more what exactly qualifies as sharp. I think it's pretty sharp even at 600mm but others think it is soft. Maybe my sharp is their soft and they're used to a different kind of sharp. In the end, how could we ever value anything without putting numbers on it?
youre naive to think the 150-600 is sharp at 600mm. anyone would know its limits are around 400-450. after that use it only if you must but be aware of its limitation. you didnt think you could pay $1000 and get a 600mm thats killer sharp, did you? its acceptable but not in a pro range. even a 400 2.8 AFS cropped to the 600mm the tamron can do is sharper.
its with every lens you buy. every zoom has its weaker side and stronger side of the focal range. this is 101.
same with cameras. they say the D3S can do native to 12800, but you must consider the images arent going to look excellent and are a use under extreme circumstances.
same with shooting a lens wide open. no lens is great wide open as it is stopped down even 2/3 of a stop which can make a huge change in performance from open aperture.
for me numbers means nothing. I stick to reputable reviews. if theres a mixed bag of assessment of the gear in question, I wait. read as much as I can then decide if I want it.
how do I know what I think is sharp for me and whats for others? I look at their work, simple as that. if I see the persons pictures and they offer raw downloads as well, then I decide for myself. its quite simple to me. better than dxomarks numbers anyday. let me see the actual files in full raw and I will judge myself.
I very much believe that dxomark gets payed and the tests reflect that a bit here or there. I do not think they are honest. like many including KR. they may look professional because their website gives a feel like its a lab that does expertise assessment. but to me I see right though it all. after all, I am a photographer. my eyes are trained to see BS.