That's not really true. Wellington had a great reputation as a sporting city through the late 90s and most of the 2000s with the Canes in their pomp, the 7s, the Phoenix, some cracking Warriors games, and cricket at the Basin. They've only really declined similar to how going to live sport has declined throughout NZ. We're in a weird situation where pay tv is happy with their numbers but the crowds are staying away.
Yeah the Canes drew pretty well the better part of 20+ years ago, but their crowds have been inconsistent and fickle over their life time.
The Phoenix have never been a big draw, not by NRL standards anyway. Most seasons they'd have had a sub 10k average, and though things have been looking more up recently their numbers have been absolutely abysmal at times. Put it this way, an NRL side wouldn't be viable if they were expected to survive off the Phoenixes numbers long term.
The rest are largely irrelevant, one off events, semi pro, etc.
Also, the Caketin is not as bad as you're making out, it's a tiny oval, so in the scheme of the majority of NZ sports grounds the seats are generally pretty good (I'd rather sit in a Caketin corner than a similar sport in a rectangle). It only lacks when comparing it with the proper rectangles and there's only really two of them Dunedin and Hamilton (and soon to be Chch unless they stuff that build up).
It might be good by NZ standards, but it is that bad by Australian and NRL standards. The club would be starting out in one of the worst home grounds in the league outside of some of the trashiest of the suburban grounds in Sydney and Bruce.
Ovals like the Cake Tin are a massive drag on rectangular sports, and an NRL side would already be a relatively risky prospect in a relatively small, relatively competitive, market like Wellington. The NRL needs to get expansion into NZ right the first time, and should make sure that things are as ideal as possible before having a crack at a market like Wellington, and the Cake Tin simply doesn't meet the standards the NRL should be setting.
Also, I don't want to turn this into the other thread but why do you think they could get by on (partially) poaching rugby talent? There really isn't that much rugby talent getting poached. Most are already league players. The biggest poach in recent years in Thompson and he was a club (amateur) midfield back.
As I said above I don't want this to descend into the other thread, but, league might be the better product for you, it's not for the majority of NZers.
There's a massive difference between suggesting that they could poach RU talent and saying that they could get established first graders.
They'd absolutely be in a position to offer some young blokes fresh out school a fast track to professionalism and a starting position with a solid wage. They'd also be well positioned to poach some outsiders and journeymen who've never really cemented themselves in RU and might be better suited to RL. We'd only be talking about a handful of their top 30 as well.
Yeah they'd be searching for diamonds in the rough, just like every club does from time to time, but it wouldn't/shouldn't be a long term necessity, just a way to get by while they establish their juniors pathways which isn't as straight forward as many people assume.