Symond's bowling was trash but the kind of trash that was common place in the middle overs through the 90s and early 00s. He was the 5th highest wicket-taker for Australia over his career, and went at a decent enough economy (5.01) for a part time bowler in that era. For comparison - during Symond's career, the likes of Chris Cairns, Sachin Tendulkar, Paul Collingwood, and Yuvraj Singh all had similar economies. Watson's (4.86) wasn't significantly better, tho he clearly was more of a wicket-taking threat.
A lot of Symond's poor economy rate is also down to the fact that he got targeted a lot more by opposing batsmen. They weren't about to score runs against McGrath, Bracken, Gillespie, Lee, Warne or Hogg, so they chanced their arm against Symo, and he did a decent enough job to ensure that he didn't consistently got a 6s and 7s. He finished 75% of his spells with an economy of 6 or under, and in the process allowed Australia to field batting right down to 7, and added a ton in the field.
I'd be interested in seeing his bowling stats for overs 15-40 only, or when he came on to bowl with the opposition side in a bad position. Couldn't find a way to filter for all that though. Maybe later.
In the context of an ATG team, it really does depend on what ruleset the game is played under. In modern-day ODIs, he would get slaughtered. Just 4 men out in the deep during the middle overs and he has to work with a newer harder ball. We've got smaller boundaries now too. If you're picking an ATG side for modern day ODIs, you need 5 proper bowlers. No way around it. But for ODIs of the 90s to the 00s, Symonds was a legit asset. Batsmen who can bowl filth and got at less than run a ball were all the rage.
Hussey is a good shout for the ODI/Aus ATG XI too btw. Slightly superior all-conditions batsman to Symonds, and you don't lose much in fielding. If you've got enough bowling options in your side already, then he slots in well.