Every country has to start from somewhere to catch-up with the others in longer times.
I don’t think IAF will induct more than 100 Tejas, until 2025, as they will test and stabilize the product for future replacements and the present order for 40+83=123 fits the bill.
Present IAF inventory has 33 sq of fighters in which Mig-21s & Mig-27s are of large numbered and to be urgently replaced and I don’t think Tejas will be able replace all of them in short span, which indeed needs time and acquisition process of single engine fighters will allow Tejas to mature.
IAF will procure 150-170, F-16s or Saab fighter for its present needs and alongwith upgraded Mig-29s and Mirage are capable enough to keep an eye on eastern border.
I dont see f-16's until U.S offers something strategically. Gripen or f-16's will take atleast 3-4 yrs to churn out first aircraft in india unless india directly imports them. So why not order more rafales or su-30's ?
Tejas is a last tier A/C for airforce for defending skies.