結論

laravel 5.6.3から
joinSub、leftJoinSubが使える.

$subQuery = ProfileUserView::select(['user_id', 'company_id'])
    ->whereBetween('created_at', [$from, $to])
    ->distinct();

$mostViewQuery = \DB::query()
    ->selectRaw('company_id, COUNT(user_id) AS pv')
    ->fromSub($subQuery, 'sub')
    ->groupBy('company_id');

ver 5.6.3以前

それより以前は mergeBindings使う.

$count = DB::table( DB::raw("({$sub->toSql()}) as sub") )
    ->mergeBindings($sub->getQuery()) // you need to get underlying Query Builder
    ->count();

こんな感じ

$subQuery = ProfileUserView::select(['user_id', 'company_id'])
    ->whereBetween('created_at', [$from, $to])
    ->distinct();
          
$mostViewQuery = \DB::table(\DB::raw("({$subQuery->toSql()}) as sub") )
    ->mergeBindings($subQuery->getQuery())
    ->selectRaw('company_id, COUNT(user_id) AS pv')
    ->groupBy('company_id');

ただしmergeBindingsは、bindするパラメーターの順序を気をつけないといけないので注意する