R1a isnt the only y haplogroup associated with proto Slavs. I2a is clearly slavic and present among all slavic populations. Czech people are not more genetically slavic than Belarusians, sviatogor knows this, he knows more than me or anyone on here about genetics. However, Western Ukrainians may be the original slavs and they are considerably more similar to czechs and slovaks and in the case of slovaks many are identical. If this is true then slovaks are very slavic genetically.
of course slavic is a cultural term that is being superimposed on a genetic ethnicity. Proto slavs may have been genetically diverse we just dont know at this point.