They'd have been more expensive too, particularly important given the lifespan many type 1s ended up having, a 20 was more or less in type 2 territory for length and weight already if you compare it to a 24 for example. For size, weight and purchase cost you'd be firmly in Type 2 territory for them all, so you might as well built more type 2s..... It can't have been too much of a disadvantage otherwise I'm sure BR wouldn't have ordered more in the mid 60s and would have gone for type 2s like the 24 instead.
Regarding 17s though, I've heard people comment that unlike most type 1s they've poor vision in BOTH directions, as neither gives you a particularly good view of what you're going to couple to.