can we consider that Tag Heuer and Omega are direct competitors (reputation, prestige, quality, movement etc) because they are in the same range of price?

Nope, it's not that simple. Although TAG and Omega have in the non-near past been great competitors in many arena's, and more recently been marketing toward a very similar market segment, to say they are in direct competition is probably a little bit on the simplistic side.

Omega has over the past three or four years dropped a significant chunk of their entry level models (like the Dynamic) and have introduced a new tier of higher end movements and models in what appears to be a concerted migration of their products "upscale".

TAG-Heuer on the other hand, while they have introduced a number of models with the Calibre 36 (an El-Primero based movement), has downgraded some of the classic product line models due to LVMH (the conglomerate that owns TAG-Heuer and Zenith)'s inability to get certain movements from Swatch Group (which owns Omega), and re-introduced a couple of entry level watches in the F1 line. TAG-Heuer seems to be looking to expand their niche a little moreso than Omega is.

There is a certain degree of overlap in the market segment Omega resides in as compared to TAG-Heuer, but there are plenty of areas where there isn't direct competition.

Also, is the stainless steel used for the Tag Heuer S/el Link is the 316L as the new f1?

I'm not sure I understand your question due to it's phrasing. However, I am not conversant with the specifics of the Stainless Steel TAG-Heuer uses.

-- Chuck