It wasn't so much a slight on Davidson's behalf as it was a compliment to Wasim 414 wickets is one hell of an acheivement, over twice as many as Davidson. Davidson did manage to play Test cricket for ten years, so it's not like he never had a career of any length. I'm just saying that Wasim's much superior number of wickets probably cause him to be considered a better bowler than Davidson, fairly or not.
I honestly don't know that they do, TBH. I think Davidson is routinely considered automatically inferior to the likes of Lindwall and Miller who had relatively similar tallies. While this
may be true, it also may not be.
I think the main reason virtually no-one ever remembers Davidson is that, apart from taking wickets at a phenominal rate, there wasn't really that much to remember him for. If Glenn McGrath had been as quiet as him, he might well be suffering a similar fate in 40 years' time.
You've presented a different argument, as we were talking about seam bowlers, and I never once mentioned spin bowlers needing to be in an attack to add variety. Spinners have other qualities that sometimes fast bowlers can't produce. All batsman do struggle with high-calibre bowling, that's correct, but Wasim was well capable of bowling at such a standard. Factor into that the angle at which he was bowling, which can cause uncertainty in a batsmans mind, and then perhaps he can be as effective as some of the other bowlers mentioned.
I only mentioned spinners because I couldn't think of another left-arm seamer than Wasim or Vaas (and I don't want to use them as I've argued in the past that both have qualities superior to McGrath).
Either way - I just think there were bowlers capable of that bit more than Wasim, who'd cause that bit more trouble than him, not because they bowled with the left-arm, but because they bowled with that bit more relentlessness.
Variation does aid a bowling attack. The South African team of the past few years is a perfect example. Makhaya Ntini, Shaun Pollock, Andre Nel plus two or three other fast bowlers. They've made an effective bowling unit, yes, but what is often missing is a high-class spinner, or somebody who bowls at a different angle to the right-arm medium-fast bowlers that South Africa have in abudance. Eventually a batsman will get used to the ball coming from the same area, and that is where a left-armer can be very useful, to change the angle of attack.
The trouble the SAfricans have had is nothing to do with a spinner and everything to do with the inconsistency of their seamers. Pollock was oft-written-off as gone until last season; Ntini has still to convince most people on all surfaces; Nel has still to hold down an undisputed Test place for long. They never had anything like these troubles when they had Donald, de Villiers, Matthews and McMillan, nor Donald, Pollock, Kallis and Klusener, because these 4 were all top-class.
Of course variety
can aid an attack, but it can do no more than turn a potent one into that bit more potent. A rubbish left-arm seamer is a rubbish left-arm seamer, and his variation will do far more harm than good. The same applies to fingerspinners and wayward wristspinners.
Sure, he was brilliant, but there were quite a few more so, even if you don't believe Imran Khan was one of them.
O'Reilly and Marshall never played for Lancs!
And Barnes would kinda fill that role anyway.