West Indies have an awful batting line-up and tons of bowling. None of your arguments hold water. Why give a team like Bangladesh hope? Grind them into the dust. Bangladesh don't have the mentality to bat for a draw
West Indies should have looked at scoring 750-800 runs in the match. As it happens they may even lose with that 800 - that would be somewhat freakish. The quickest way to score that many runs is to increase the aggression past 500. You lose far less time that way than declaring at 527 and having to bat to 250 or so - which you might not even get but you certainly can't bat with any great freedom. If you bat with freedom past 500 then you get runs quickly. If you make it to 600-650 then you're almost certain to be safe, you maximise time left in the match and you set a much tougher follow-on target. If WI wanted or had to bat again then they spend less time consolidating or batting with low aggression.
To put it another way you can get those 100 runs batting with total freedom against a knackered attack on a less worn pitch in the first innings, or you can get them in the 3rd innings when you're worried about losing wickets, which will then have a knock-on effect to the rest of the innings.
Ignoring the fact that teams will get bowled out trying to score say 250 instead of 150 - I reckon it would take you another 40 overs to score 250 instead of 150 simply because the first 100 out of 250 will typically be batted normally at around 3 an over - and then you'll lose 2-3 wickets typically as well - which effects the rest of the 150 runs you get. So 30 or so extra overs initially and a few more because of the 2-3 extra wickets and so greater consolidation potential and/or less able batsmen at the crease.