The tendonitis is often more painful than the SLAP lesion. What's tough is figuring out if it's possible to improve your tendonitis with the SLAP present. There are different degrees of SLAP lesions and how well you can rehab one without surgery is heavily dependent on how structurally stable the glenohumeral joint is. The less stable the joint is the more the rotator cuff has to work and the harder it is tho give the tendonitis the rest it needs to recover. One of your PT friends might be able to do some stability testing on you to help figure out how stable the joint is. That would give you a better idea of what to expect.
So I'd look at the pros and cons.
If you have surgery now, you'll recover faster overall but you're not likely to have a full race season and might have trouble training to prepare for this season.
If you don't have surgery now and you currently have a raging tendonitis, it's likely you'll need at leats 6 weeks to recover from that, you'll lose training in the meantime but may be able to salvage part or all the season.
Let's say you decide not to have surgery, continue to train and end up either blowing out the shoulder further or not being able to finish your season due to pain... you will have gained part of the season that you could early on, then you'll end up with surgery and out for the rest of the season.
Or, you might make it through the whole season, if you can get the rotator cuff under control and you can get it repaired at the end of the season or not at all depending on what happens.
Something else to keep in mind:
This type of shoulder surgery carries more than just a slight risk and you need to discuss this fully with the surgeon. I do see a proportion of shoulders that don't do well after surgery and end up with very little gain or sometimes worse. These are a small minority but speak frankly with the surgeon about it if you're going ahead.
Living life like there's no tomorrow.
http://gorgebikefitter.com/
2007 Look Dura Ace
2010 Custom Tonic cross with discs, SRAM
2012 Moots YBB 2 x 10 Shimano XTR
2014 Soma B-Side SS