Its about budgets, both on development and on procurement and operational costs. The Su-27 series and the F-15 are relatively expensive jets to procure and operate, and the F-16C (or F-16A MLU) are a good middle ground budget wise.<p>The F-5E&#x2F;F Tiger [0] was one of the most under appreciated fighters on the market in the 70s and early 80s. The was limited in A&#x2F;A victories in real combat because of lack of opportunities, although successfully used at TOPGUN and FWS at a low operating cost. Although marketed as a LWF, The F-5 was actually a multi-role aircraft, and used in combat as a strike aircraft.<p>IMO the F&#x2F;A-50 [1] is the most under-appreciated advanced 4th gen fighter on market. At around $30m its half the cost of a new F-16, although a refurbished F-16 is viable for budget constrained Air Forces.<p>[0] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Northrop_F-5" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Northrop_F-5</a><p>[1] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;KAI_T-50_Golden_Eagle" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;KAI_T-50_Golden_Eagle</a>