Wolf-
Laining in a vacuum may be considered bittul Torah compared to what you could be learning… but that doesn’t mean you shouldn’t be doing it ever. Someone needs to lain in shul, and the pashtus is tzorchei tzibbur is docheh Talmud Torah if you are needed. Also, if you are laining to enable you to memorize pesukim to aid in your learning down the road, than that probably wouldn’t be considered bittul Torah.