It's not the worst comparison as both have been relative journeymen managers and both tend to play 4-2-3-1 where possible. However, stats and statistics show that Pellegrino isn't even as good or 'exciting' as Silva. Firstly, Silva sticks to the 4-2-3-1 whilst last season Pellegrino used a 5-4-1 (admittedly to good effect) last year a fair amount.
Secondly, for all of those wanting am exciting, free-scoring Saints, Pellegrino isn't your man. His teams have averaged 1.16 goals/game over his career, much lower than Silva's 1.74 goals/game. Admittedly Pellegrino has a better return than Pule last year (with 1.07), but only marginally so.
Thirdly, Pellegrino's win% is much lower than Silva's (43% compared to 55%), and only marginally better than Puel's (by 0.5%). You also have to remember that Pellegrino (Alaves excluded) has managed relatively big teams like Valencia and Independiente.
Finally, to the best of my knowledge, Silva has never been sacked for on-field results (an indicator of his quality?), whilst Pellegrino has.
It's not the worst comparison, but when you look at the numbers, Pellegrino seems to be a bad choice for a club and fans who want a more exciting brand of football IMHO.