On point one, it's my opinion that Howe's achievements outweigh Silva's. You evidently disagree. That doesn't make my opinion wrong.
On point two, you obviously haven't read my 2nd sentence properly. Check again and note the comma's. 'To then stay there, comfortably,'. He's stayed in the Premier League comfortably.
On point three, every manager makes poor signings over a 4 year period. Marco Silva signed the likes of Andre Gray, Brown Ideye, Kamil Grosicki and Will Hughes for over £40m.
Howe has also brought in the likes of Ake (£20m) Fraser (£400,000) Josh King (£3m) and Callum Wilson (£3m) and made a massive profit on players like Mousset, Ritchie and Mings.
In any case, he's spent a fraction of what everyone else has spent and got them in a position where now they're considered a steady mid-table team.
Coyle and Laudrup had one good season in the Premier League, they aren't in Howe's league. He's precisely the path to follow for young managers, to take a team from League One to a steady Premier League team across 5 years, without the resources generally required to even attempt it, is a hell of an achievement - I'm not sure why you'd attempt to knock it.