Is there some strategy for dealing with bosses before rocket turrets, nukes and railguns.

I am about 120 warps in at 30% evolution and cannot stay at any planet longer than ~13 minutes as a boss comes and simply destroys everything. The amount of resources to destroy it seems to be excessive. No problem with the bosses existing, just wondering if they are too many, too soon with too much health. Maybe have another layer of bosses that are about 1/10 the current strength.

For comparison, a Big Explosive Biter has 375 health while the lowest boss biters have 50000 health. Assuming ~60 damage/second/laser turret it would take 83 turrents 10 seconds to kill that one boss while they spawn every few minutes or so.

It was similar in the Warptorio expansion but there were additional techs that increased damage, made mobility easier with gates, provided a way to see where the boss was and didn't auto-target the platform unless pollution was bad.

There was increase in upgrades for artillery. Initial vision was, that the boss would be something that forces you out of the planet in early game and in late game gives you some challenge as well (since everything else can be solved with flametrowers)

The range of bosses is greater than rocket turrets and railguns.... Just sayin

What is the counter to bosses, just curious. Are we expected to do quality defenses to get extra range? As it stands, the spitters will just stand off you base and kill everything because they outrange all defenses.

Yes quality is answer to basically everything later on (I actually like that it is more important that in a base game)
I was actually using artillery for those bosses later on as well (rail-guns would be better)
Another option that you have is to place landmines with bots as well.
Last option is also to use spidertrons to help as well (that one is super fun)

I would say that that is more that a few options