Lalu didn't do the groundwork for the speed upgrade of BPL Shatabdi. That credit goes to his predecessors, particularly Nitish Kumar. The track and signalling upgrades, and extensive track renewals were carried out during Nitish Kumar's term. Even the indigenous manufacture of LHB coaches was done during Nitish Kumar's term. The official speed up in 2006, was nothing but an formal inauguration of the service using the upgraded rolling stock and utilizing the upgraded route.
While he does deserve credit for a lot of his work during his term as an RM, he gets a lot of undue credit for his predecessor's efforts. A substantial share of Lalu's accomplishments on freight loading, running more trains, increasing...
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freight revenue were due to Nitish kumar's spending on infrastructure, the restructuring that was started during his tenure as RM and a favorable market. As usual, people doing the background, non-fancy work are rarely appreciated.
But of course, Lalu deserves credit for smart freight fare structuring, effective management of bureaucrats and most importantly, building on the work of his predecessor, rather than ignoring it like many other RM's did.
And there is no use speculating on what he 'could have' accomplished. The growth in the first half of his tenure, was accompanied by a decline in the 2nd half. Facing corruption charges and after losing power in Bihar, Lalu had the motivation to redeem himself in the public opinion.