He is 6'1" and 233lbs, so not all that small, but I understand the visual observation.
He is getting the job done and filling a void.
On a side note take a look at KC,s two starting LBs.
Anthony Hitchens - Dallas Cowboys 2014 round 4 pick 19
Damien Wilson - Dallas Cowboys 2015 round 4 draft pick number 28
and check out the numbers they are putting up.
Both drafted by the Dallas Cowboys and both starting for KC, man the past regime made some serious mistakes at LB letting those two get away, and seems that KC just sat back and harvested two really good LBs at our expense.
Not like Hitchens or Wilson are pro bowlers, .and both are still liabilities vs pass. They are decent LBs, nothing more.
Thomas is a serviceable LB too, He's not overpowering and he's much better when he is freed up to run vs taking on
and he has enough speed to factor in coverage.
But what is showing up clearly is he has much instincts than Jaylon Smith
Seems to always be in position more than Jaylon.
jaylon can keep talkin about complex scheme but no matter who the DC is, he still looks lost, mis-guessing into gaps,
and he's not fighting thru traffic enough for some one who was so highly touted coming into the NFL 2016 draft class.