My first 2 Cockers, Josh and Sam, were both entire males with a 22 month age gap between them. Josh was the older one and was always very laid back with other dogs and very confident. Sam was quite reserved with people he didn't know and a bit anxious generally. I think that was simply because he was unwell when a puppy and missed out on a lot of socialisation. The two of them got on well, although they were never best buddies.
I now have 7 year old William, castrated at 15 months because of an undescended testicle and 2 year old Louis, who is entire. William is very confident, not very interested in other dogs and generally accepts anything new that happens in his life. However, after 5 years of being an only he really didn't want to share me with Louis and spent lots of time upstairs on his own at first just to keep out of the way. Broke my heart to see my lovely boy so unhappy
and I regretted getting Louis, especially as he turned out to be a very needy and difficult puppy.
2 years on and they get on reasonably well. Louis would like William to play with him and snuggle up, but William won't. When I sit on the sofa I have a Cocker either side of me and they're both relaxed that way. They've both learned to adapt to each other and quarrels are rare and so far have been a bit of grumbling and handbags. However, I reckon that it's a precarious relationship sometimes and I observe them quite a lot and give them both time apart sometimes.
So I think it really depends on the personalities of both dogs and although it works out in most cases there are no guarantees.