You've pointed out the work of a union, rather than the work of a union leader.
There's very little doubt that he ensured that the members of the RMT were well looked after during his tenure, which saw it's membership quadruple.
Whether you were happy about his methods is frankly irrelevant.
A small point of correction, membership increased by more than 20,000 to 80,000 (i.e. from around 60,000), it didn't quadruple:
Under his leadership, the RMT's membership increased by more than 20,000 to 80,000.
Source: http://www.bbc.co.uk/news/uk-26527325